Swapped Yellow & White Bulkhead connectors -- Damage????

[nkemp]

I goofed. The question is how big. I swapped the YELLOW & WHITE (Lower RH one) connectors at the bulkhead and tried to start the car (for the curious... it doesn't start that way). The reason is that my car (Early: #897) did not come with a YELLOW connector. Instead it is WHITE with a yellow dot on the bulkhead connector and the dot on the wire harness likely fell off long time ago. Living in a world where connectors are keyed I wasn't watching for the potential swap.

Now I appear to have troubles:
- The Battery light is on (even though the car is charging) (GM alternator of some vintage)
- Tach points towards 7000RPM at idle
- No voltage shown on the volt gauge.
- There may be more that I've not ID'd yet

So the questions for the "wise ones" are... What damage occurred and associated repair do I need to do?

FWIW I have also posted on DMCHelp.

Too bad I can't post this one anomalously,
Nick

[dmc6960]

Hmm, start by checking every single fuse. I'll need to look at the pinouts for a little bit...

[DMCMW Dave]

Hmm, start by checking every single fuse. I'll need to look at the pinouts for a little bit...

My answer would be the same - without comparing the two conectors and what-if-ing the connections (12 V power to the tach feed? etc.) it would be very hard to predict the failures. If Jim doesn't come up with anything by Monday I'll have a go at it.

[dmc6960]

Alright, you may have just blown fuse #5, but check them all anyways. It also appears you connected the 12v idle motor output of the idle ECU to the (-) side of the coil, and vise versa the (-) from the ignition computer to the 12v idle motor output from the idle ECU. This unlikely hurt either computer, and may have just blown fuse #1. It also appears you may have shorted out the idle speed thermistor with the 12v feed for the otterstat. This could be responsible for blowing fuse #5, and may have also damaged the thermistor which could affect your idle speed.

The dash symptoms all seemed to be related to no power into the dash. Do the other lights like oil pressure and brake light turn on without the car running but ignition on? If fuse 5 is out, I believe power would be fed into the dash through the battery light, illuminating the battery light, and providing enough leakage power to mess with the tachometer, while leaving all the other lights and volt meter dark.

[SS Spoiler]

I think Dave should get Jim to move to Chicago and work for him. Now that would be a team!

[Bitsyncmaster]

I also did that swap accidently and tried to start the car. But mine had no problems after I swapped it back.

[David T]

Without trying to figure out a fault tree for this I would just deal with the damage. Write up a list of all of the problems and attack them one-by-one. Some may be multiples of the same problem and one fix may solve 2 (or more) problems. As pointed out you may have blown some components like the tach and the alternator. Checking all of the fuses is a good place to start.
David Teitelbaum

[Ron]

If you happen to have blown the tach, I have one that only needs the precision resistor...PM me.

[nkemp]

First off, thanks to all for the help and camaraderie. It is appreciated! I was feeling pretty low and not thinking clearly.

The #5 fuse was blown and replacing brought back the all the dash services. Tach is fine. Battery light is working again... I was afraid I took out part of the alternator. Big smiles there. No other fuses blown.

Idle is not so smooth. Oscillates between ~500 & 1500 rpm... and as I recall it is the same with and without the AC. Based on Jim's feedback, that leads to Idle Control Unit or thermistor. The first thing I'll do next is to make sure the thermistor is connected. It can be reached from the back without taking off the intake manifold.

The good news is that the main reason I was working on it (running rough) seems to be fixed... runs much smoother. Not sure if it was a vacuum leak or ignition related. I also found a slight coolant leak in the VOD. Normally the plugs would have fallen into position at the bulkhead due to the wire preset. But I had split the loom and got rid of the path over the engine. Much tidier. But in doing so, the connectore were free to float around and is how I swapped them.


I also did that swap accidently and tried to start the car. But mine had no problems after I swapped it back.

Thanks for posting that Bitsyncmaster. It gives me some sense of comfort in that I have good company. (I was going to comment that I wasn't the only dummy that did that but I decided it didn't sound right :) )

[dmc6960]

Great to hear Nick! If your thermistor is still connected it could be "burned out" making the idle ECU think it's not even there. To check it, check for some resistance between the two pins. You can do that from the bulkhead connectors. Just put it back correctly this time!

Check the black-slate wire and black-yellow wire in the "white" connector. The bulkhead diagram lists 14.6k ohms at 52degrees F. Unsure what it would be at 75deg.

[nkemp]

Thermistor measures about 1.6K at some hot temp (I drove the car a half hour ago or so).

So I'm guessing it is good. Also, as I recall, thermistors are dissimilar metals welded/bonded together. If current flows through a thermistor it will produce heat. So I doubt that the thermistor was damaged by any current.

I pulled the connector to the idle speed motor and started the car. It ran perfectly smooth at 1000 RPM. I connected the plug and it starts hunting in the 500 - 1500 RPM range.

And yes the white connector in in the right spot... easier not to mess up when you pull one at a time :-)

[Bitsyncmaster]

That kind of idle hunt, I would first suspect the idle motor is sticky. Clean the valve part in solvent.

[dmc6960]

That kind of idle hunt, I would first suspect the idle motor is sticky. Clean the valve part in solvent.

That makes sense. If the ECU wanted to slightly open it up and it stuck, it would continue to try and open it up until it finally snaps open. That that point it's too far open, the engine surges, and the same happens in reverse.

[nkemp]

I used brake cleaner to clean the idle valve. When I reinstalled RPM was steady ... at 2500RPM. When I pulled the connector it drops to 1500RPM. When I had the valve off, I noticed that the off position allows air through the valve which I don't think is right.

I have a second air valve from a later model Volvo ( the smaller size valve, non-black model). It did not seem to work any better but I'm not sure if the valve worked when it came off the car.

Does anyone have a pinout for the valve and can it be powered directly to actuate it and see if it works?

[nkemp]

So I found one reference to the Bosh valves indicating that the center pin gets 12Vdc and by grounding one or the other pins it opens or closes the valve.

[Bitsyncmaster]

So I found one reference to the Bosh valves indicating that the center pin gets 12Vdc and by grounding one or the other pins it opens or closes the valve.

That is correct.

[DMC5180]

It happens so fast there is no way to accurately test it. just OPEN/CLOSED with power. The valve should move very freely. so much so that you can quickly shake (snap back and forth) the ISM in your hand. You should be able to here the valve CLICKING(slapping OPEN and CLOSED)

[nkemp]

I found a site that teaches diagnosing the Bosch 3 wire idle air valve. It is summarized here for all that follow:
- Check the valve resistance at the connector outer to outer and it should be about 40 Ohms
- Mine is about 21.1
- Check valve resistance center to side. Each should be about 20 Ohms. Mine are 9.9 Ohms & 11.2 Ohms
- With ignition on, engine off, check for voltage present on the plug's center terminal. Mine measures 11.1 Volts
- With the ignition on, engine off, connector attached, verify that the valve is buzzing. Mine does

If one of these tests fails you have a problem. But it sounds like all can pass and yet you may still have a problem.

Note that the spare valve, a 501 version, measures 43.2, 21.6 & 21.4 Ohms

So my numbers are not great but it does not appear to be a bad valve based on this part of the diagnosis. It may be that the valve we use (??500 series???) may have a different resistance reading.

Also, from what I've read, the Bosch 500, 501, 516 & 520 Idle Air Valves are all interchangeable.

[Bitsyncmaster]

The Volvo unit draws about half the power of our stock ISM. So your resistance reading sound correct.

[nkemp]

Today it is working perfectly...@&^%!!!!! I hate intermittent problems!

The only clue I got was that I decided to re-Ohm the thermistor and it indicated an open circuit. I checked the resistance multiple times at the plug and they indicated open. I wiggled wire bundle near the IAV and I think the circuit closed and reoppened and closed. Not trusting a sample size of one I tried replicating and now I get a constant reading.

You know how it goes ... one hand is trying to make two probes contact the connector which is floating in air, the other is wiggling wires on the other side of the car and you are reading the meter which is poorly lit and poorly positioned to the right. Was it me or was it the car? So I started the car and idle is where it should be with a slight bit of hunting ... maybe +/- 50 RPM. Intermittent connections sounds probable.

[nkemp]

I took it for a spin. When it started idle RPM was nice. After driving for a bit, when it was at idle, it was hunting from about 500 - 1500 like before. Very consistent rhythm. So it appears at low temp, idle is fine and when it warms, idle gets out of control. Seems to me that only three things affect this:
- Idle Air Control Valve ---might it be sticking when warm ---probability of this being the problem seems low
- Idle Speed Control Unit --- Without swapping a unit I'm not sure how to tell if this is bad
- Thermistor --- Damaged and now signals a bad temperature curve --- again, how to tell without swapping

[nkemp]

Another drive and it seems the mode of operation is:
- Starts & idles fine
- As it warms the idle starts hunting 600 - 1500RPM
- At some point, presumably full operating temp, idle is 2500 RPM

When I checked the resistance at the bulkhead, the reading indicates open circuit. This time, moving the wires near the IAC valve does not change the reading.

[Bitsyncmaster]

An open thermistor in the idle circuit would result in 2500 RPM. When the engine is cold the idle motor is open about 1/4 open. When the engine is hot the idle motor is almost closed. Curb idle setting and mixture vary how much the idle motor is open. You can play with the curb idle screw to see if that helps.

[nkemp]

Ahah.. it did it again ... the thermistor was reading open and when I moved the wires near the valve it showed resistance. Note that when the engine was hot, moving the wires did nothing.

Looks like it would be worth while to rewire the thermistor wire. Before rewiring I can open the loom and check to see if I can find the break.

Where do you guys get color coded wire if I need it? I know it is not a requirement but I would like the color codes to match the diagrams. I've searched in the past with no luck.

[nkemp]

Progress... but I'm not ready to declare victory yet ... here is what I've found for those with high idle problems

One of the two female connectors in the wire harness connector body attached to the thermistor was loose and backing out of the connector. Likely, in the past, it had enough force to just touch male pin on the thermistor but over time and with my moving the wires it eventually receded from the connector. It took a while to realize this since I was getting a good reading when I used the probes to verify wire integrity (the VOM probes were going in far enough to reach the receding socket. When I connected the wire to the thermistor no reading. Yet the thermistor read fine by probing its pins. Eventually I noticed one connector in the female socket was further recessed than the other. When I pulled on the wire it came out totally. FWIW ... it looks as if it has been that way forever since the retention spring was perfectly flat to the body.

I pulled back the rubber boot, bent up the spring, pushed it through the boot and reinserted it in the connector. Reconnected the connector and everything reads fine. Now to reinstall the intake manifold & fuel injection.

BTW ... I've been using split braided wire loom. So far I like it. Looks better than the split corrugated plastic stuff and a LOT easier to use that the non-split braided loom. I think the only problem is that it will retain dirt/dust.

[nkemp]

I solved the 2500 RPM issue but it is still hunting from about 600 to 1500RPM. I suspect the 600 bottom end is set by the curb idle setting. So what to do:
- Swap out the Idle Air Valve
- Swap out a Idle Speed Controller
- Swap out the thermistor (I really don't want to take off the top side again! Besides, at mostly warm the resistance dropped to about 1.3K Ohms from the 9K+ Ohms when at ambient ~81F)

[Bitsyncmaster]

I solved the 2500 RPM issue but it is still hunting from about 600 to 1500RPM. I suspect the 600 bottom end is set by the curb idle setting. So what to do:
- Swap out the Idle Air Valve
- Swap out a Idle Speed Controller
- Swap out the thermistor (I really don't want to take off the top side again! Besides, at mostly warm the resistance dropped to about 1.3K Ohms from the 9K+ Ohms when at ambient ~81F)

It's not the thermistor causing the hunt. Your resistance readings sound about right.

[nkemp]

I'm tempted to get a new controller and change that out first just because I don't want to fight with the brass tube off the air valve.

Any Volvo 240 or 260 controller (that is 4cyl or 6cyl) should work ... shouldn't it?

[nkemp]

I changed out the original idle air motor/valve to a "501" model (new, smaller and compatible with ours as best I can tell). The engine runs perfectly smooth at about 1800 RPM. Not what expected:
- If only the idle air motor was bad, then a new motor should have brought the RPM to spec (about 800)
- If only the controller was bad, then changing the motor should not have resulted in any changeMi

Could it be that the motor and the controller are both bad?

I did check for air leaks by spraying brake cleaner at the usual suspect. No change (except for cleaner parts).

[Bitsyncmaster]

I changed out the original idle air motor/valve to a "501" model (new, smaller and compatible with ours as best I can tell). The engine runs perfectly smooth at about 1800 RPM. Not what expected:
- If only the idle air motor was bad, then a new motor should have brought the RPM to spec (about 800)
- If only the controller was bad, then changing the motor should not have resulted in any changeMi

Could it be that the motor and the controller are both bad?

I did check for air leaks by spraying brake cleaner at the usual suspect. No change (except for cleaner parts).

I run the smaller Volvo idle motor (not sure of the number). I found it runs much smother than OEM idle motors.

I would leave the Volvo motor in your car and now you can fix the high idle. Start with backing out the curb idle setting and see if that idle speed drops. Verify your idle switch is working and your vacuum advance is off at idle.

[nkemp]

Advance is off at idle. Idle switch works. More details in next post (2 posts to correct formatting and readability)

And I concur that the new motor runs better. Quieter and smoother (determined by feel) ... and fits perfect using its mounting bracket

[nkemp]

After an overnight cool-down, when it started it idles about right where it should or a bit high (but under 900). As it warms the idle speed creeps up towards the 1800 range. FWIW, when I pull the FV connector, RPM drops to about 1000 but the engine does not run smooth and performs more poorly when driven.

I haven't touched the curb idle for a couple reasons.

It idled in the correct range a couple weeks ago ... so mechanically it should be correct
When it starts from cold, it idles about right ... as such it can get down there


As I see it:


There are only two things electronic that affect engine RPM:

The Idle Speed Control controlling via the Idle Speed Motor
The Lambda Circuit (measuring oxygen in the exhaust stream) controlling supposedly minor RPM variations via the Frequency Valve.


Two things electrical+Vacuum

Vacuum advance of the distributor

there is also the distributor input to the ignition control


The WUR


For mechanical only you have:

Throttle plate position
Air leaks




Working backwards:
- Checked for air leaks... none apparent
- Nothing has changed relative to the throttle plates and control. Besides, when cold it does idle about right
- Ignition seems to run well at any throttle position
- WUR tested OK a couple weeks ago before latest problems. As I understand it these are designed to increase gas flow at cold so it should not drive idle up at higher temp
- No vacuum at distributor when idling

That leaves Idle Control & Lambda.
- Thermistor... resistance drops with temperature increase. Presume curve is correct.
- Idle Speed Switch tests OK
- Idle Speed Motor... installed 2nd one, eliminated hunting. Can control in approximately correct range when cold.
- Lambda...Not sure. (I recall a test where a battery is used in place of the Lambda... need to chase that test down for details)
- Lambda control... engine seems to run well at all road speeds
- Idle Speed Control Module... ???? No good way to test I'm aware of. Need to swap a good unit.
- Does the Idle Speed Controller fail such that it increase idle speed as temperature increases and throttle switch is open?


So that is where my car and my head are at this Monday morning.

[Bitsyncmaster]

If you removed the intake, then your curb idle and idle switch adjustments have changed.

It sounds like all you need to do is back out that curb idle screw a little.

[nkemp]

If you removed the intake, then your curb idle and idle switch adjustments have changed.



The fuel assembly with throttle body comes out as a unit. The curb idle and idle switch do not get removed from the fuel assembly. The only related part that gets disconnected is the rod to the throttle spool. So I don't understand how the curb idle or idle switch would have changed.

Let me add...I remove the two screws securing the fuel assembly to the intake manifold and I remove the "W" pipe. Next I disconnect the rod at the throttle spool and disconnect the airline and electrical connections. I free the fuel injectors from the ports, disconnect the fuel lines at the cold start, fuel supply, fuel return & WUR and loosen the FV. (I think that is everything) Then the whole assembly lifts out intact.

[dmc6960]

I agree that in principal the adjustments should not have changed, but reality say otherwise. I would suspect all adjustments and start by backing off the throttle stop and seeing how it behaves.

Keep in mine relating to your 900rpm cold start - a cold engine needs more power to run. So a hard-set adjustment that gives you 900rpm when cold could easily give you 1800rpm when hot. All adjustments should be done on a hot engine.

[DMC5180]

Nick, you have by-pass leak some place. I had similar situation once. My ISM had frozen in position (partial open) over the off season. The first start of the season It fired right up at seemingly normal idle. After a minute or two the idle started climbing (from reduced friction) it topped out between 1800-2000 rpm. With ISM unable to close (regulate the RPM) it was the equivalent having the idle by-pass screws open. I'm not saying this your problem just giving you a comparison for your symptom.

[nkemp]

Nick, you have by-pass leak some place. I had similar situation once.

Where was your leak? I spayed brake cleaner around the fittings and all I got was cleaner parts ...the RPM's never changed.

[Bitsyncmaster]

Would take 30 seconds to back out that curb idle screw.

[nkemp]

With the curb idle screw I can back it off to about 1100RPM (As I write this I'm wondering if the cable or linkage was restricting its travel). Took more than a little adjustment... a couple turns maybe. When the fans started running, idle went to about 1000. With AC it is lower yet.

For the about 25 years I've had this car, idle was fine. Right where it should be. Something happened in the last week or so that changed that and I'm having troubles rationalizing curb idle adjustment even though it brought it down some. Adjusting curb idle seems to be compensating for something else that has changed (such as the idle air controller controlling different so that it is passing more air. Or an air leak somewhere and we are balancing it out by closing the butterflies a bit). As an interim it is OK but I think there is a primary cause somewhere else.


Nick, you have by-pass leak some place. I had similar situation once. My ISM had frozen in position (partial open) over the off season. The first start of the season It fired right up at seemingly normal idle. After a minute or two the idle started climbing (from reduced friction) it topped out between 1800-2000 rpm. With ISM unable to close (regulate the RPM) it was the equivalent having the idle by-pass screws open. I'm not saying this your problem just giving you a comparison for your symptom.

Dennis I think I misread your post. Your fix was not a leak but freeing up the ISM.

[Bitsyncmaster]

If you need to back the curb idle screw out all the way then you have a problem of the throttle plates are not closing or your deceleration springs are bad. Mine had bad deceleration springs and with the curb idle screw backed out fully the idle would be fine at 775 RPM until the engine got warmed up. Then the idle was about 1000 RPM.

But verify your throttle cable has a little slack when in the idle position.

[nkemp]

SUCCESS! I do believe that it runs better than ever. I hate it when a post ends and there is no resolution to the problem. So here is what I did:

I removed the 501 version of the Idle Air Motor/Valve from the engine

This is the next version of our motor (500 I think) and found on later PRV Volvos. FYI, there are two newer versions since the 501.
I switched to that motor because it seems to operate smoother, draws less current and is the next generation of ours.
I did to the old 500 IAM what I described below so I'm now sure it would work as well.


I cleaned it again (3rd time) with brake cleaner. Note that the cleaner came out about as clean as it went in.
I carefully manually worked the valve back and forth. It felt a little sticky
I sprayed the valve insides with PB Blaster.

For those thinking WD40 ... It may clean it out but WD40 is not really a lubricant (I think it is fish oil). It was initially intended for Water Dispersal.


When I got the valve I also took the harness (a good rule of thumb for salvaging all electrical components). I connected the center wire to 12Vdc and then tapped the other leads alternating one at a time to the engine causing the valve to open and close. I did this a number of times to exercise the valve to its max in each direction. Under normal use, it may never travel that far and thus may be more sticky at the extremes.
I closed the valve and sprayed a bunch of PB Blaster inside and let it soak for over supper. When I came out it had leaked through (it is not a liquid tight seal when closed. Next time I'll fashion a plug so that it doesn't leak out).
Repeated the electrical actuation of the motor/valve


At this point I installed it in the car and took it for a spin. I drove it on the local highway and would periodically depress the clutch and let off the gas. Idle was dropping to about 775RPMs and stayed there. But I noticed that it was dropping to about 500 RPM, bouncing back up to 775 and then leveling out... and in one case it actually dropped past 500 & died. I let out the clutch in 3rd and it fired back up without a whimper.

I took it home and reset the curb idle (Ihad backed it out as part of an earlier effort to diagnose) to where it was (about 775RPM or a bit lower) and took it for a spin. Now idle does not drop as far (best I can tell there is enough lag in the circuit that the idle control does not do well on engine decelerations from 3000 RPM to idle that fast which is why it was dropping past 775RPM to 500RPM with the curb idle backed out). It now runs PERFECT...smooth, nice idle... I don't think it ever ran that nice. It actually runs better at throttle. When back, since I wanted the belt & suspenders package, I pulled the W pipe and cleaned the decel springs in the throttle plates. They were clean and not sticking.

Based on my experience, I recommend periodically cleaning the idle valve and lubing it. I think this is related to a lot of idle and performance issues these cars see due to age, use and lack of use.

Also, for those who are seeing very high RPM, that can occur when the Thermistor is out of the circuit. In my case you can read about it above but in short was due to one of the two female connectors not properly retained in the socket and it had backed out. Initially it made contact by touch but eventually it got pulled out so far that it lost even that amount of contact. I can only imagine what the signal to the Idle Control Unit looked like when it was making intermittent connections.

Now on to the next item....

[nkemp]

One question is ...Was this related to the miss-wired bulkhead connectors?

I wonder if the crossed wiring resulted in the valves being driven to their extremes which may not be normal operation ( I suspect they operate in a subset of the full range). In doing so they experienced the crud at the extremes that "gummed them up" causing poor motor response and thus idle problems (hunting due to over compensation by the controller). That's my theory.

[DMC5180]

Dennis I think I misread your post. Your fix was not a leak but freeing up the ISM.

Correct! What you did to free yours up is exactly what I'd to get mine working again. I used 3-n-1 machine oil on mine and worked the valve back-n-forth till it was really freed up. Worked like charm after that.

With the valve being stuck in a fixed open position it was the equivalent of an internal by-pass air leak. Your sticky/stiff valve would cause the idle to be slow to react and overshoot the target RPM. Remember it competes with the completely independent lambda circuit (FV) too.

[DMC5180]

One question is ...Was this related to the miss-wired bulkhead connectors?

I wonder if the crossed wiring resulted in the valves being driven to their extremes which may not be normal operation ( I suspect they operate in a subset of the full range). In doing so they experienced the crud at the extremes that "gummed them up" causing poor motor response and thus idle problems (hunting due to over compensation by the controller). That's my theory.


Under normal circumstances, if you turn the key too the RUN position the ISM Valve will be driven FULLY CLOSED and slowly go FULL OPEN in about 5 seconds. The Idle ECU thinks the engine is in an under speed situation and it opens the valve to compensate. So it does do a full sweep from time to time if for some reason you don't turn the engine over right away with the key ON. Probably more often than you think.

[nkemp]

Update: Drove the car today to a car show about an hour away. Today it is idling at about 1500 RPM. The idle is steady but high. It was the same idle speed when I returned from the show. With AC on it drops to about 1000 RPM.

What is confusing is that the other day I drove it quite a bit and the idle was perfect at about 775. So what changed?

I'll get it warmed up again and check curb idle and linkages just to be sure. ... THese checked OK and it doe not appear that there is a mechanical problem causing high RPM's.

Question: Might the O2 sensor need replacement & if so could it be driving the fuel mixture high resulting in high RPM's?

[Bitsyncmaster]

A rich mixture will help idle run faster but the constant idle system should have enough adjustment to compensate. Maybe you have the bad deceleration springs. Can you post a photo of the springs. If the spring are not evenly spaced they seem to be the bad ones.

[DMC5180]

Update: Drove the car today to a car show about an hour away. Today it is idling at about 1500 RPM. The idle is steady but high. It was the same idle speed when I returned from the show. With AC on it drops to about 1000 RPM.

What is confusing is that the other day I drove it quite a bit and the idle was perfect at about 775. So what changed?

I'll get it warmed up again and check curb idle and linkages just to be sure. ... THese checked OK and it doe not appear that there is a mechanical problem causing high RPM's.

Question: Might the O2 sensor need replacement & if so could it be driving the fuel mixture high resulting in high RPM's?


If you push the Idle micro-switch while the engine is running at 1500, does the RPM drop or just stay at 1500? 1500 is the typical RPM you get if the Micro-switch is not being tripped. The LOAD with the A/C and Fans running will pull the idle down ,as you say, to about 1000 rpm. This is a typically worn or misadjusted linkage issue. The Linkage rod needs to be shortened slightly.

[Bitsyncmaster]

If you push the Idle micro-switch while the engine is running at 1500, does the RPM drop or just stay at 1500? 1500 is the typical RPM you get if the Micro-switch is not being tripped. The LOAD with the A/C and Fans running will pull the idle down ,as you say, to about 1000 rpm. This is a typically worn or misadjusted linkage issue. The Linkage rod needs to be shortened slightly.

+1

If the idle switch is not working then you get vacuum advance and that will bump the idle about 400 RPM higher.

[nkemp]

- Pushed the Idle Switch and no change in RPM.
- Changed the O2 sensor no change and maybe a bit higher (needed to be changed anyway and they are on sale at Advanced Auto ~$15) BTW ... the sensor came out relatively easy. The hard part was making the wiring connection.

[nkemp]

Here's a clue: Sprayed brake cleaner in the vicinity of the Idle Air Motor and the RPM's decreased...Yup decreased. So I pulled the hose located on the Idle Air Motor connecting to the brass tube. Tuns out it had developed a leak /tear since I put it back on. When I pulled the newer 501 Idle Air Motor off the Volvo a couple years ago I took the hose with it... just-in-case. Here is a photo of the DeLorean (short) and the Volvo hose (long. Volvo must use a shorter brass tube):
20410

The brass tube that connects to the air/fuel assembly is cut at an angle (not square to end). The existing hose does not go on the tube very far. Using the Volvo part, I cut the hose about where the red line is and it is a lot longer than the original. Since it slides on farther you are not in as much risk of cutting the hose on the end of the angled tube when the hose clamp is tightened.

These hoses must take a fair amount of abuse. The original (which is ONLY 32 years old!) is now easily damaged. The Volvo part indicated that it is easily damaged also. When I cut the hose with a scissors style tube/hose cutter it nicked the tube a bit and a crack developed going up the hose length. I had to cut it off again a ways back to stop the tear. Brittle is not the correct word to use but they are not robust like they should be. I think I'll be looking for a replacement just-in-case.

So the original hose likely failed after the test drive where I had claimed success above. Spraying cleaner on the hose may have cooled and shrunk the hose just enough to lessen the airflow and thus decreased the RPM's. For whatever reason, the brake cleaner I'm using is not good at finding vacuum leaks because it didn't cause the engine to rev.

SUCCESS Maybe...now idle is about where it should be. This turns out to be an example of how multiple related issues conspire to complicate the issue.

THANK YOU to all for assistance, an ear and camaraderie.

[DMC5180]

Nice Find. Never heard of that particular one before. Obviously it can happen though. The rubber on these cars won't last for ever. Where was the crack in the hose? So how bad was your pipe of agony to re-install?

[nkemp]

"Pipe of agony" ... that is putting it politely! In this case I was VERY careful not to remove the pipe. I seat the o-ring and brass ring when the fuel assembly was off the engine. A correct size long socket makes a nice tool to seat the ring. Installing the pipe is not terrible difficult the first time. My problem, and I presume others, it that when the pipe is removed the brass ring and o-ring may come off with it and getting those back is a PITA while it is assembled on the car.

One of the reasons I pulled the Volvo hose was I was thinking about a better way to connect that tube but never pursued it. The thought was to permanently install a tube to the air port and use a longer rubber hose to connect. That said, I did not ever determine what the clearance issues would be relative to installation and removal of the air & fuel assembly.

The original hose was cracked about a 1/2" from the end connected to the brass tube. It tears relatively easily likely due to its age. It was likely caused by the hose clamp & may have been aggravated by the angle cut on the tube.

[DMC5180]

Now I understand your perspective to avoid the POA. I've had that pipe out many times over the years and never considered it that big of a deal. I never had to deal with the brass cup ring/o-ring falling out though. I have replaced the o-ring once for good measure, but the whole metering unit was out at the time.

[SS Spoiler]

Nick, back in 94? when I blew a head gasket, I elected to get a crate engine from Don Steger- DeLorean Motor Center. I found that the POA was replaced with a pipe fitting and a long rubber hose with a right angle bend in it. Maybe it was a late fix for an early problem. Anyway it makes assembly much easier.

Paul Cerny #2691
Kalispell, MT

[DMCMW Dave]

Nick, back in 94? when I blew a head gasket, I elected to get a crate engine from Don Steger- DeLorean Motor Center. I found that the POA was replaced with a pipe fitting and a long rubber hose with a right angle bend in it. Maybe it was a late fix for an early problem. Anyway it makes assembly much easier.

Paul Cerny #2691
Kalispell, MT

I've seen that on some crate engines. Volvo design change at some point.

[nkemp]

Your brass rings stay in? Mine comes out really easy as indicated above. Dave, or others, would a replacement ring have a tighter friction fit?

[DMCMW Dave]

Your brass rings stay in? Mine comes out really easy as indicated above. Dave, or others, would a replacement ring have a tighter friction fit?

Don't need to replace it, just deform it so it is a tighter fit.

[nkemp]

Don't need to replace it, just deform it so it is a tighter fit.

Good point. I always thought it was that way by design. Next time I take it apart I'll "tighten it up".