How much air does the idle speed motor move?

[Michael]

I'm trying to diagnose a poor cold idle situation. Once the car goes into closed loop everything is perfect, but cold idle is another story. It's very low and sometimes dies. I have searched and there are a ton of threads which lead me to check for vacuum leaks first. None yet so I moved on The CSV works perfect. The idle air motor is vibrating...no clicking, just a vibration but I decided to pull it anyway and when the key is in run position it vibrates but no detectable air movement through the passage. Is that normal operation?

[tommyrich]

The idle control valve is like a faucet, it has a gate that opens and closes proportionally to the electric field applied to it. IIRC it receives a 100Hz signal from the controller. The opening of the gate is proportional to the pulse width of the 100 signal. The vibration is the magnetic field swithing at the 100Hz rate. So the gate can move anywhere from fully open to fully closed. If you take it out, the gate should move freely with no voltage applied. If not, it may be stuck.
Hope this helps,
Tom

[Bitsyncmaster]

First thing to check is that there is no ignition advance. You can test that just by pulling the hose off the distributor advance and starting it cold.

Have you adjusted the mixture via setting the duty cycle with a dwell meter? That setting will affect the mixture when your in open loop (cold engine).

The WUR keeps the cold engine very rich if working properly. Best check of that is a wideband reading the AFR on the tailpipe but most people just use the control pressure readings to see if they match the book values.

Does your idle hold 775 RPM consistently with the warmed up engine?

[Michael]

I don't have a dwell meter (yet). But yes, The idle is rock solid once warmed up. I will reconnect it tonight and pull the dist. advance hose and see how it starts.

[NightFlyer]

You can try cleaning the idle air motor (CIS) with carb cleaner. In fact, I just pulled and cleaned mine a couple days ago because it was sticking causing slight surges during non-throttle events (gear changes, stop and go situations, etc). Courtesy of K-Jet.org:


Spray a bunch of carb cleaner in it and plug both of the ends. Now, shake it up as much as you can – up and down and roll it between your hands like you were trying to make a long snake out of Play-doh like in kindergarten. When you roll it, you should be able to hear it clicking back and forth. If you can’t hear anything moving in there, keep cleaning it or get a new motor. Make sure to shake out all of the excess carb cleaner and let the thing dry for a bit before you re-install it.

[DMCMW Dave]

Two fast idle motor tests.

1 - Open up the driver side electrical compartment and locate the idle ECU (the black one on top). Start the engine. Pull out the plug closest to the center of the car. The idle should take off to about 2200RPM. Plug it back in and it should settle down. If this works, the ECU and the idle motor are good.

2 - Remove the hose between the idle motor and the cold start injector. Look down the throat of the idle valve. Have an assistant turn the key to the run position but do not start the car. The valve should immediately open up all the way, and then over about a 30-second period gradually close all the way. This shows that the valve is good, not sticky, and the electronics are working.

[NightFlyer]

Good tests - thanks Dave :thumbup:

I'll be performing these on my car tonight :biggrin:

[Michael]

Thanks Dave! Since tthe idle valve is already loose I will do the second one first.

[Michael]

OK, the idle speed motor stays closed. I can freely move it open and shut by shaking it and when closed, it remains closed. When I started it open, it closed and stayed closed. I did this first on a bone cold engine then I reinstalled the motor and tested the ecu. With the ecu unplugged idle did indeed rev up and settled down when plugged up.

Bitsync (I would call you Dave but that would be confusing to dmcDave). I pulled the vacuum advance on the cold idling engine...nochange. Now I thought there was supposed to be no advance uuntil it went to closed loop, but you asked so I complied. No change. Now on the other hand, once the engine is warm, pulling the advance line does hurt the engine smoothness.

So what do you think? New idle motor for sure and a vacuum solenoid just to play it safe? PS. Could find no leaks in the lines themselves. Also just noticed when charging my compressor there is a random miss once warmed up...smooth as silk warm.. but random miss when warm...which is really leading me to the vacuum solenoid.

[Bitsyncmaster]

You should have no advance with the throttle closed (cold or hot). I guessing you were reving the engine warm and found no advanced hurt that. That would be normal.

If you got advance with a warm engine at closed throttle then it may just be your idle switch or solenoid.

If your running the engine with the ISM not installed, it's operation would depend on the engine RPM. The test is not run the engine, turn the key to on and watch the ISM.

[NightFlyer]

OK, the idle speed motor stays closed. I can freely move it open and shut by shaking it and when closed, it remains closed. When I started it open, it closed and stayed closed. I did this first on a bone cold engine then I reinstalled the motor and tested the ecu. With the ecu unplugged idle did indeed rev up and settled down when plugged up.

Bitsync (I would call you Dave but that would be confusing to dmcDave). I pulled the vacuum advance on the cold idling engine...nochange. Now I thought there was supposed to be no advance uuntil it went to closed loop, but you asked so I complied. No change. Now on the other hand, once the engine is warm, pulling the advance line does hurt the engine smoothness.

So what do you think? New idle motor for sure and a vacuum solenoid just to play it safe? PS. Could find no leaks in the lines themselves. Also just noticed when charging my compressor there is a random miss once warmed up...smooth as silk warm.. but random miss when warm...which is really leading me to the vacuum solenoid.

1) Correct - the vacuum advance should only be operable when the engine is warmed up, above 104F.

2) Even when warm though, you shouldn't be getting any advance at idle, as that's what the micro-switch is for. So if you're experiencing advance at idle, then something isn't right - screw that activates micro-switch may need adjustment, loose wires, defective micro-switch, or bad solenoid.

I'm interested to hear what Dave S has to say about the idle air motor, as I don't know how often those go bad, but obviously something isn't right if it's not opening up at idle.

[DMCMW Dave]

Sounds to me like the vacuum hoses are backwards. You should have no vacuum to the solenoid cold, it should be going to the warmup regulator.

Look at the diagram glued to the engine cover. The vacuum switch under the intake has 3 ports. Vacuum is switched to the regulator cold and to the solenoid hot. The center port is the source for the other two ports. You can check this by feel (on a cold engine), but you can't see the vacuum switch.

When warm, the vacuum goes to the solenoid but is turned off at idle (microswitch). If you pull the vacuum hose off at idle nothing should change. The vacuum leak to the engine when you do that is VERY small.

If the solenoid is stuck open (normal failure mode) you will have vacuum at the ignition distributor at idle, which makes the spark WAY too advanced and it will run rough and/or idle too fast if there is enough air getting in.

Make sure everything is working as designed before you adjust anything.

If this has been wrong a long time you may have the base timing set very retarded if it was set with vacuum advance engaged.

[DMCMW Dave]

1)

I'm interested to hear what Dave S has to say about the idle air motor, as I don't know how often those go bad, but obviously something isn't right if it's not opening up at idle.

His test by pulling the wire verified operation of the motor. It will be nearly closed at idle if the static idle (i.e. the stop screws) is set properly for a hot engine.

[Michael]

OK just so everyone is clear. I did check the ism off the car and hooked up..my wife turned on the switch withoutcranking just as Dave said and it stays closed. If I manually open it and turn on switch it slams shut and stays shut. Afterward I did reinstall the ISM before starting the engine cold to test the ecu. I did pull the advance line and rev it to around 2 to 2.5k and held...ran fine cold.

The microswitch is adjusted correctly and does work.

[Michael]

Sounds to me like the vacuum hoses are backwards. You should have no vacuum to the solenoid cold, it should be going to the warmup regulator.

Look at the diagram glued to the engine cover. The vacuum switch under the intake has 3 ports. Vacuum is switched to the regulator cold and to the solenoid hot. The center port is the source for the other two ports. You can check this by feel (on a cold engine), but you can't see the vacuum switch.

When warm, the vacuum goes to the solenoid but is turned off at idle (microswitch). If you pull the vacuum hose off at idle nothing should change. The vacuum leak to the engine when you do that is VERY small.

If the solenoid is stuck open (normal failure mode) you will have vacuum at the ignition distributor at idle, which makes the spark WAY too advanced and it will run rough and/or idle too fast if there is enough air getting in.

Make sure everything is working as designed before you adjust anything.

If this has been wrong a long time you may have the base timing set very retarded if it was set with vacuum advance engaged.
Thanks Dave. I will check it tonight and see if i can see or feel anything out of place.

[DMCMW Dave]

OK just so everyone is clear. I did check the ism off the car and hooked up..my wife turned on the switch withoutcranking just as Dave said and it stays closed. .

If it closes immediately as you describe, I'd suspect a problem with the ECU but I've never seen one do that. At this point I'd substitute a test unit (which you probably don't have handy). It should swing wide open on that test, and close over about a 30 second period.

One more thing - Check the 3-wire plug that goes to the idle motor. If one of the pins has backed out of the connector (or is corroded/green) stuff like this will happen.

[NightFlyer]

Thanks Dave. I will check it tonight and see if i can see or feel anything out of place.

Regarding the advance - you stated that pulling the advance hose (from the solenoid to the distributor) while idling cold yielded no change. But when you did the same thing once warmed up, it changed the idling noticeably. Did I get that right? If so, then I'm still of the opinion that it's the micro-switch, the solenoid, or the electrical connection between the two that's causing that problem. You can check the grounds on the back of the intake runners - make sure that they're clean and making good contact. Also check the connection between the micro-switch and the solenoid, making sure that their isn't any corrosion and that everything is making good contact.

[Michael]

Regarding the advance - you stated that pulling the advance hose (from the solenoid to the distributor) while idling cold yielded no change. But when you did the same thing once warmed up, it changed the idling noticeably. Did I get that right? If so, then I'm still of the opinion that it's the micro-switch, the solenoid, ...
Yes that's right. I could feel no suction on the line either (when cold). But when warm it does pull vacuum. So the solenoid valve seems to be working.
I'm going to check a few things Dave suggested once I get a shower...still sweaty from my run. The engine should be back to ice cold again so I can check that vacum port. I will then write a complete up to the minute history so there will not have to be any going back and reading previous posts.

[NightFlyer]

Yes that's right. I could feel no suction on the line either (when cold). But when warm it does pull vacuum. So the solenoid valve seems to be working.
I'm going to check a few things Dave suggested once I get a shower...still sweaty from my run. The engine should be back to ice cold again so I can check that vacum port. I will then write a complete up to the minute history so there will not have to be any going back and reading previous posts.

Actually, that means that the thermal switch is working. Thermal switch opens when the engine temp is 104F, which then sends vacuum to the solenoid. That vacuum is either released onward to the distributor or confined to the solenoid based on what the micro-switch is telling the solenoid to do - when the micro-switch is closed (activated) at idle, it's supposed to confine the vacuum to the solenoid, when the switch is open during throttle, it's supposed to send the vacuum onward to the distributor to cause the advancing of the ignition.

So, for some reason, the solenoid is releasing the vacuuming onward to the distributor, even though the micro-switch is telling it to hold the vacuum. Thus, the problem lies with the micro-switch, the solenoid, or in the electrical connection between the two. I'd start by checking the connection. Then you can test the switch with a meter to see if it's sending the right signal to the solenoid. That should tell you what the exact cause is and allow you to remedy it.

Sounds like your hoses are on the three port properly. If they were mixed up (on backwards), then you should have been getting vacuum during your cold idle, which you weren't. If you wanted to check this though, an easier way than feeling your way around under the intake manifold is to pull the vacuum line at the CRP when cold idling - you should have vacuum there when cold idling. Doing this might even cause the car to die, which again, would confirm that the hoses on the three port are hooked up properly.

I think that Dave S either misread or misinterpreted your post of the tests you performed with the vacuum advance line.

[Michael]

Thanks Josh and Dave. I'm uploading a video that tells everything...think it's easier this way and relays the information better.
http://youtu.be/HrwoUUGEFO8

http://youtu.be/HrwoUUGEFO8

[NightFlyer]

Thanks Josh and Dave. I'm uploading a video that tells everything...think it's easier this way and relays the information better.
http://youtu.be/HrwoUUGEFO8

http://youtu.be/HrwoUUGEFO8

Video is set to private.

[Michael]

Video is set to private.

fixed. Thanks in advance for taking the time to watch this everyone.

https://www.youtube.com/watch?v=HrwoUUGEFO8

[NightFlyer]

Green striped wire on top, solid black on the bottom is the correct hook up for the micro-switch - so you're good there.

Either the micro-switch is defective, the solenoid is defective, or there's a problem with the electrical connection between the two. Start by inspecting the connections at both the switch and the solenoid, making sure that everything is clean and making good contact. If that doesn't do anything, then put a meter on the line that runs into the solenoid and see if the switch is doing what it's supposed to be doing - then you'll know if it's the switch or the solenoid causing the problem. You can also check the grounds on the on the sides towards the back of each of the intake runners - make sure that they're clean and making good contact.

As for the idle air motor (CIS) - I honestly don't know enough about them, except that it's a relatively simple device. Like Dave said, I'm leaning towards a bad connection with the ECU (or possibly even a bad ECU) - check the plug and connector to make sure that everything is making good contact. I also don't know if it's normal to be able to shake the valve open - when I had mine off and cleaned it, I wasn't paying that much attention to what it was doing inside, but I believe that it stayed relatively stationary, despite all the shaking and rolling around that I was putting it through. I have to charge up and re-install my battery before I'm able to do much more testing with my idle air motor.

[Elvis]

OK, the idle speed motor stays closed. I can freely move it open and shut by shaking it and when closed, it remains closed. When I started it open, it closed and stayed closed. I did this first on a bone cold engine then I reinstalled the motor and tested the ecu. With the ecu unplugged idle did indeed rev up and settled down when plugged up.
....


ECU broken, power stage transistor defect !

OR - a wire from the ECU to the ISM makes no connection.

but 90% sure - typical power stage problem.

[Michael]

Is it possible the vacuum solenoid can be at fault? I just went out to start it cold again and I pulled the vacuum line of the WUR just to see Iif there was vacuum there. There was but not much. I'm going to mess around with some carb spray after work today and probably order a solenoid for starters.

[Spittybug]

I'm agreeing with those that say it is the idle air controller itself or the upstream ECU. It isn't your vacuum advance solenoid.

If you diagnose it to be the ECU, talk to me before buying a new one. As I am no longer K-jet, I have one to let go cheaply.... I must have sold the idle air controller though, I can't find it.

[Michael]

I'm agreeing with those that say it is the idle air controller itself or the upstream ECU. It isn't your vacuum advance solenoid.

If you diagnose it to be the ECU, talk to me before buying a new one. As I am no longer K-jet, I have one to let go cheaply.... I must have sold the idle air controller though, I can't find it.

Thanks Owen. I'm going to work some more on it tonight. If I can't find any definitive answers in the form of huge vacuum leaks, I'm going to see if Dave has a used test ecu that I can "borrow" if I pay shipping both ways. I've got to place an order for some misc. items anyway like a compressor label, screw and other small stuff.

[DMCMW Dave]

Another issue one to check. I've see the idle speed micro switch turn into a resistor. It should read wide open or dead short. Sometimes they will fail such that the read about 60 ohms when it should be closed.

In this case it confuses the ECU, sometimes works the solenoid etc. In other words - idle gets erratic and will change from time to time.

Easy to test with an ohm meter.

[NightFlyer]

There shouldn't be much vacuum at start-up or idle - but the presence of vacuum at the CPR during idle indicates that the hoses are hooked up correctly on the three port under the intake, so no need to check that further.

Whenever chasing electrical gremlins, I like to start with the easiest thing first. It may be stupid, but you might want to try pulling and re-seating fuse 1, if you haven't already.

Both the idle air motor (CIS) and vacuum solenoid receive their instructions from the idle ecu. As both are currently malfunctioning (and seemed to fail together at the same time), it's highly probable that the fault lies with the ecu. But as Dave S. said, you can still check the switch with a meter to confirm that it's functioning properly.

Absent that, swapping out the ecu for a known good ecu is your next best test.

Best of luck! :thumbup:

[Michael]

Awesome, thanks Dave and Josh. I will get my multimeter out and check it tonight...along with a few other things.

[flux3d]

I had the exact same problem with my car last year. Starting up I had to keep my foot on the gas and raise the revs until the engine warned or it would run really rough and die. I pretty much followed the exact same problem path add you've done, but in the end it was the ecu which was malfunctioning. At cold it was shutting the valve on the idle speed motor and starving the engine.

In the end I borrowed a known working ecu from another owner, plugged it in and sure enough problem solved. After that I carefully opened up the ecu, desoldered all of the IC chips on the board and replaced them with chip holders (to make it easier to replace the chips in the future) and then new IC'S.

The first time I plugged it in and turned the key she started better than ever! :) talk about a good feeling. Not an easy job to do but we'll worth it.

If you need details on the components I used pm me. I think I have a diagram somewhere.

[Michael]

Put my multimeter and was pulling 80 ohms closed but that's not what got me...just moving the blade connector a little I could hear it tripping on and off. I put my finger on it and it went crazy on and off. I think the positive connection blade has broken inside the switch case because the blade is very loose.

It still may be the ecu but I will try the switch first and go from there.

[NightFlyer]

Put my multimeter and was pulling 80 ohms closed but that's not what got me...just moving the blade connector a little I could hear it tripping on and off. I put my finger on it and it went crazy on and off. I think the positive connection blade has broken inside the switch case because the blade is very loose.

It still may be the ecu but I will try the switch first and go from there.

Yeah, that's not good.

Hopefully that will solve your problems :thumbup:

[Michael]

Well got my micro switch in today and no luck...still cold idle problem. It does a little better however, if it makes any sense it's smoother, just still idling too low. Just like always, once warmed up idles perfect. Hopefully Dave has a used "test" ecu I can borrow just so I can eliminate that being the problem. I know the micro switch was bad but I'm pretty sure it's either the ECU or Idle motor as well.

[NightFlyer]

Well got my micro switch in today and no luck...still cold idle problem. It does a little better however, if it makes any sense it's smoother, just still idling too low. Just like always, once warmed up idles perfect. Hopefully Dave has a used "test" ecu I can borrow just so I can eliminate that being the problem. I know the micro switch was bad but I'm pretty sure it's either the ECU or Idle motor as well.

Probably ECU...

But here's another thought - would a failure of the diode in the fuse/relay compartment possibly be causing these problems? I'm not sure how you'd check that, so maybe someone else can elaborate on this possibility if they think it's viable...

[Michael]

Probably ECU...
Yeah I'm leaning towards that too especially since so many owners have posted here and been down this road before with the same problem, and the ECU fixed it. That and I watched the idle motor close shut upon a cold start and never move.

[NightFlyer]

Yeah I'm leaning towards that too especially since so many owners have posted here and been down this road before with the same problem, and the ECU fixed it. That and I watched the idle motor close shut upon a cold start and never move.

While I'd definitely try swapping ECUs at this point, if you haven't put a meter on the anti-feedback diode in the fuse/relay compartment to check it, then I'd definitely do this as well.

The microswitch is shared between systems/functions and the diode prevents feedback interference between those two systems/functions. What got me to thinking that it might be the diode is how you have the idle air motor problem AND the vacuum advance problem happening at the same time. Not sure if there are any specific tests that you can try in trouble shooting whether it's indeed a diode failure, but you can at least check the diode with the diode function on your multimeter and make sure the connections there are sound.

[Bitsyncmaster]

If your car will be a DCS, I can lend you an ECU (my micro design) to try.

That goes for anyone that wants to try it.

[Michael]

Thanks Dave but sadly another DCS will pass me by.

Thanks for the advice Josh. I just tested the diode and I'm pretty confident in saying it's bad too. I was only reading anywhere from 0 to about 15, but when even I was reading any kind of drop, say 10, I could touch my leads together and get the same reading. It's hard to keep my meter zeroed out. In other words I was getting no drop whatsoever.

I'm going to see if I can find it locally so I will not have to wait 3 more days.

[NightFlyer]

I'm correcting myself here - the diode that I previously referred to is in the ecu compartment behind the driver's seat, and NOT in the fuse/relay compartment behind the passenger seat.

[Michael]

I'm correcting myself here - the diode that I previously referred to is in the ecu compartment behind the driver's seat, and NOT in the fuse/relay compartment behind the passenger seat.

I know, but you have been so helpful I didn't have the heart to correct you. :reading:I knew what you meant and went right to it.

[Ron]

I just tested the diode and I'm pretty confident in saying it's bad too. I was only reading anywhere from 0 to about 15, but when even I was reading any kind of drop, say 10, I could touch my leads together and get the same reading. It's hard to keep my meter zeroed out. In other words I was getting no drop whatsoever.

I'm going to see if I can find it locally so I will not have to wait 3 more days.To test the diode you need to set the meter on ohms/resistance, disconnect one end of the diode, take a reading, reverse the meter leads, and take another reading. One way should read near zero and the other very high or infinite...

If the idle speed system is operating at all, the diode is not causing an idle problem (It couldn't be blown open else the system would not activate, and, if it was shorted internally, it wouldn't matter because that circuit would be grounded anyway. Off idle would be another story...

[Michael]

To test the diode you need to set the meter on ohms/resistance, disconnect one end of the diode, take a reading, reverse the meter leads, and take another reading. One way should read near zero and the other very high or infinite...

I have a diode setting on my meter.

[Ron]

I saw that in an earlier post......but the thing is you were talking about "drops" etc which makes no sense to me (that is with voltage) ...and you have to disconnect one end of the diode regardless of which method you use to test it...
With sugar on top :wink:

[Michael]

I saw that in an earlier post......but the thing is you were talking about "drops" etc which makes no sense to me (that is with voltage) ...and you have to disconnect one end of the diode regardless of which method you use to test it...
With sugar on top :wink:

I completely removed the diode before testing it. The diode setting measures the voltage drop instead of the resistance.

[Michael]

I suspected my cheap MM wasn't acting right so I used a friends MM to test with and it checked out good. Instead of reading 0 it was reading in the 900 range, so instead of ordering a diode I'm getting a decent multimeter.

[Ron]

The diode setting measures the voltage drop instead of the resistance.
Forward voltage drop....
So, one dead horse27149 and a wild goose -- Next! :devil:

[Michael]

Forward voltage drop....
So, one dead horse27148 and a wild goose. Next! :devil:

My apologies I thought "forward" would have been implied.
27150
diode test on my MM. The same test on a friends yielded over 900 and out hooked up reverse. So it's good.

[Ron]

My apologies I thought "forward" would have been implied.
Not needed at all! ...I was wondering because of "any kind of drop" and that the diode wouldn't cause the problem, so I tried to cover all bases.
It's hard to tell when it's reading too much into/missing a key symptom. (Makes for a lot of spare horse grease tho! ;-)

If all of the other suggestions play out, you might try watching the WUR/CPR pressures as it warms up??

[Bitsyncmaster]

The diodes that were used in our cars have been reading 0.7 to 1.0 volts on my meter. They really have improved diodes of today. Most all new diodes have a 0.6 volt drop and Schottky diodes are even better at 0.3 volts or less.

[NightFlyer]

The diodes that were used in our cars have been reading 0.7 to 1.0 volts on my meter. They really have improved diodes of today. Most all new diodes have a 0.6 volt drop and Schottky diodes are even better at 0.3 volts or less.

I did some trouble shooting on my car a while ago and tested the idle diode.

First, my multimeter is an older digital made in South Korea Sunpro by Actron Cp7678 (as opposed to the newer iterations of such model, which are made in Taiwan and China). The original MSRP was $99.99, and it was stickered for retail sale at $79.97. Admittedly, it's no Fluke, but it's also light years better than the el cheapo made in China/Taiwan/Philippines/etc. I was able to pick it up NOS for only $12 shipped. Another reason I bought it is because it has independent functions for duty cycle, dwell at 4, 5, 6, and 8 cylinders, and hi and low tach for 4, 5, 6, and 8 cylinders. It has a diode testing function in conjunction with the audible tone continuity tester. Here's what it looks like:

27155

And here's what it displays when reading my idle diode -

Red lead to anode, black lead to cathode:

27157

Black lead to anode, red lead to cathode:

27156

So, you'll see that my diode has a .605 voltage drop, and is not shorted closed = a perfectly functional diode :thumbup:

[Bitsyncmaster]

I just tested the diode I removed from the idle harness and my Fluke reads 0.566 and my Extech reads 0.571 volts.

I know some of the other diodes I've checked are way higher for voltage drop. That voltage will change a little with air temp changes.

[NightFlyer]

I just tested the diode I removed from the idle harness and my Fluke reads 0.566 and my Extech reads 0.571 volts.

I know some of the other diodes I've checked are way higher for voltage drop. That voltage will change a little with air temp changes.

Maybe the 3 amp white ones found in the fuse/relay compartment...

[Elvis]

What a waste of time !

open that ECU, replace the power stage transistors and be done !
You can even use your MM to test the transistors and check which one has failed.

Use a hair dryer to open the ECU.


hugh - stupid german has spoken

[Michael]

After Dave generously donated some of his time and advice for things to check we left it at me sending him my ECU and he would test it for me. I got home and was about to do a few time consuming wiring checks but decided to go ahead and pull the ecu. It was obvious someone had opened this up before. This being a remaned car that didn't surprise me too much and I figured it had been rebuilt at least once, so I pulled it back apart to look for any red flags and saw this:
27208
This is a capacitor joint and besides being burnt looks like it leaked some. It was also just flopping around in the socket. The solder joint had broken loose and taken the etched circuit path with it away from the board. It looks like it could be rebuilt but I don't know if that's the only thing wrong with it and considering time I would spend rebuilding, I would be money ahead just ordering a new one which I did. Now to wait another weekend.

Normally I would be missing driving my car on weekends but my business has been absolutely slammed the past 4 months. Now spring is here the work has increased and I have a lot of house landscaping and the pool to get in order, so I haven't exactly had a lot of time to do anything. Even working on this idle problem gets an hour here or there of my time but never a full commitment from me. Hopefully this will fix this cold idle problem.

[NightFlyer]

After Dave generously donated some of his time and advice for things to check we left it at me sending him my ECU and he would test it for me. I got home and was about to do a few time consuming wiring checks but decided to go ahead and pull the ecu. It was obvious someone had opened this up before. This being a remaned car that didn't surprise me too much and I figured it had been rebuilt at least once, so I pulled it back apart to look for any red flags and saw this:
27208
This is a capacitor joint and besides being burnt looks like it leaked some. It was also just flopping around in the socket. The solder joint had broken loose and taken the etched circuit path with it away from the board. It looks like it could be rebuilt but I don't know if that's the only thing wrong with it and considering time I would spend rebuilding, I would be money ahead just ordering a new one which I did. Now to wait another weekend.

Normally I would be missing driving my car on weekends but my business has been absolutely slammed the past 4 months. Now spring is here the work has increased and I have a lot of house landscaping and the pool to get in order, so I haven't exactly had a lot of time to do anything. Even working on this idle problem gets an hour here or there of my time but never a full commitment from me. Hopefully this will fix this cold idle problem.

You've exhausted just about everything else it could possibly be. Hopefully whatever caused the ECU to fry didn't also fry the idle air motor.

I'm still somewhat perplexed at the microswitch and vacuum solenoid though. Did replacing the microswitch solve the vacuum advance problem at idle? If not then it's still possible that the solenoid was fried as well. Did you do a continuity check of the solenoid at all?

[NightFlyer]

You've exhausted just about everything else it could possibly be. Hopefully whatever caused the ECU to fry didn't also fry the idle air motor.

I'm still somewhat perplexed at the microswitch and vacuum solenoid though. Did replacing the microswitch solve the vacuum advance problem at idle? If not then it's still possible that the solenoid was fried as well. Did you do a continuity check of the solenoid at all?

Just to review how the vacuum advance works:

When cold (below 104F), the thermal switch (in the three port under the intake) isn't releasing any vacuum to the solenoid. When the engine temp reaches 104F, the switch opens and releases vacuum to the solenoid. The microswitch then tells the solenoid what to do with the vacuum - either keep it in the solenoid (always at idle, whether cold or warm), or release it onward to the distributor (only when warm and during non-idle operation of the engine).

Thus, you shouldn't be getting vacuum at the distributor at idle, period.

We've already determined that the thermal switch is good and that the vacuum lines on the three port are hooked up properly.

So, you need to get it warm (above 104F) at idle and see if you're still getting vacuum at the distributor or not. If you are, then your solenoid is probably bad too. If not, then it was the microswitch causing that problem, and your replacement of the switch cured it.

I know I previously said that the solenoid is controlled by the ECU, but having looked at the circuit, I believe it's independent of the ECU and simply works off the microswitch. Thus, you'll still want to check that the vacuum advance system is working properly.

Best luck!

[Bitsyncmaster]

I know I previously said that the solenoid is controlled by the ECU, but having looked at the circuit, I believe it's independent of the ECU and simply works off the microswitch. Thus, you'll still want to check that the vacuum advance system is working properly.

Best luck!

Correct. The stock ECU only uses the micro switch as an input signal. My micro-ECU will control the solenoid if you remove and jumper that diode near the ECU and remove the idle switch.

[Michael]

Thanks for the help. I did check the operation of the solenoid during warm and cold conditions by pulling the vacuum lines and seeing where the vacuum was being diverted. It was working correctly pulling the wur when cold and dist. advance when warm but I can't remember if this was before or after the bad switch replacement...probably before since it shouldn't be pulling at idle. I have not double checked it but I will wait for the ecu before checking the operation and going down any further trails.

It amazes me how well this car ran with so much wrong. Vacuum solenoid electrical connection uunplugged, idle microswitch bad, idle ecu bad, and it still started, idled fine warm and somewhat idled cold.

[Michael]

Got my idle ecu in today and popped it in. Since my idle valve was still out, I had my wife turn on the ignition and just like Dave said it should, it opened and slowly closed. I quickly buttoned everything up and as soon as I bumped the starter she fired right up and idled perfectly. I don't think it has ever done this under my care...she has always been a bit cold natured and I just attributed it to 30 year old Fi technology and a hot cam. Anyway one problem down...now to tackle the miss when warm. (Starting new thread).

Also, can a moderator maybe rename this thread so it will show up in a search for future reference? It started as a question and blossomed into a full blown idle problem, Probably title it something like "cold idle problem" or rough idle when cold...something good along those lines.

[NightFlyer]

Got my idle ecu in today and popped it in. Since my idle valve was still out, I had my wife turn on the ignition and just like Dave said it should, it opened and slowly closed. I quickly buttoned everything up and as soon as I bumped the starter she fired right up and idled perfectly. I don't think it has ever done this under my care...she has always been a bit cold natured and I just attributed it to 30 year old Fi technology and a hot cam. Anyway one problem down...now to tackle the miss when warm. (Starting new thread).

Also, can a moderator maybe rename this thread so it will show up in a search for future reference? It started as a question and blossomed into a full blown idle problem, Probably title it something like "cold idle problem" or rough idle when cold...something good along those lines.

AWESOME :thumbup:

Glad to hear it!

You reported having vacuum at the distributor when warm at idle, even though there should never be vacuum at the distributor at idle (warm or cold). You need to confirm if you do indeed have vacuum at the distributor at idle when warm. If you do, then you'll need to replace your vacuum solenoid, as it's not operating properly, as it should be holding the vacuum back at idle, and not sending it on to the distributor (it should only send the vacuum on to the distributor during open throttle events).

[Michael]

AWESOME :thumbup:

Glad to hear it!

You reported having vacuum at the distributor when warm at idle, even though there should never be vacuum at the distributor at idle (warm or cold). You need to confirm if you do indeed have vacuum at the distributor at idle when warm. If you do, then you'll need to replace your vacuum solenoid, as it's not operating properly, as it should be holding the vacuum back at idle, and not sending it on to the distributor (it should only send the vacuum on to the distributor during open throttle events.

That was the first thing I checked...it's working correctly.

[NightFlyer]

That was the first thing I checked...it's working correctly.

That's good. :thumbup:

But you still have a miss when warm - I'll watch for the new thread and see if I can help at all.