Idle Speed RPM Issue - Video Attached

[DeLorean937]

Any insight or assistance would be very much appreciated. I'm having an issue with the idle speed system with the A/C on or off. Dwell is on point and in range, well as best as I can as I am running open loop.

The car has always had issues under an electrical load. Accelerating there is no issue the car pulls like a train. The car seems to dip upon when revving the engine and returning to idle. For example while revving the engine with the A/C on you really notice a dip in the RPM as if it was about to stall and right before it does the RPM system seems to catch it. Almost coming back to idle. If you look at the video for example the issue I am having as of right now is as follows:

Car while start fine and idle for a bit then start going into a surging idle issue. If I disengage the ISM via its electrical connection the issue goes away as if everything is working perfectly. Also, I can back out the top adjustment screw and the idle will shoot up as if the ISM is connected. I can press the micro switch and idle will come down. Of course the ISM has to be connected because it should managing the idle system. Also if I try connecting the 02 sensor to activate the Lambda system this issue is the same and worse causing the engine to stall. This is kind of where I am right now. I don't know if the idle speed thermistor is the cause. I can post more videos if possible and needed.

https://youtu.be/fRdx5tVTu4I

[Bitsyncmaster]

First thing I would do is clean and oil the idle motor. It may also help to increase the lower screw (curb idle) since that helps prevent the idle plates closing to far.

Yes your idle RPM will go higher when the idle switch is off and your not in holding closed loop idle control. That is because your enabling the vacuum advance at idle speed.

[DeLorean937]

Thank you for the response! The idle motor is new and I have lubricated it. I actually have some items from you including the RPM solid state controller and I have run it in test mode watching the ISM swing open and shut. Works perfectly. Interesting about the vacuum advance I didn't realize it would stay activated while the ISM was unplugged. The vacuum advance solenoid is new also. Keep em coming I'm ready to diagnose and figure it out in case anyone has something like this issue.

Also if I lower the lower idle set screw the revving gets much worse.

[DeLorean937]

Tried raising the lower idle screw rpm came up to about 1000-1100 the surge was there also but spaced out more. Idle would try and come down but it would surge again as if someone was pressing the pedal.

[Bitsyncmaster]

Thank you for the response! The idle motor is new and I have lubricated it. I actually have some items from you including the RPM solid state controller and I have run it in test mode watching the ISM swing open and shut. Works perfectly. Interesting about the vacuum advance I didn't realize it would stay activated while the ISM was unplugged. The vacuum advance solenoid is new also. Keep em coming I'm ready to diagnose and figure it out in case anyone has something like this issue.

Also if I lower the lower idle set screw the revving gets much worse.

If your using my idle ECU, after you make a change like the lower curb idle or select another RPM you really need to let the ECU learn. It will learn if the idle is holding steady so normally you just let it idle from a cold start to warmed up after a change. What it learns is the position of the ISM at all the engine temperatures. Then it uses that table to jump the ISM to that postion when it detects your foot comes off the throttle.

Now if your problem is just idle hunting, you can select a longer delay with the DIP switch in the ECU.

[Jonathan]

I would suggest getting everything hooked-up and connected as intended and then give us a summary of what is happening (pictures, videos or just words). Without knowing the car's history or what else might be going on in the past or present, I don't find the experimentation aspect of disconnecting things and then seeing what happens particularly useful.

Get everything in your engine bay connected as shown in the vacuum routing diagram (vacuum lines and the wiring connections). Confirm all hoses are in place and snug without obvious cracks or leaks. Confirm the electrical connections are all clean, showing bare metal and then snugged in place with the metal clasps holding them so. Confirm all three of those brass screws are threaded in all the way and snug. Confirm your full throttle microswitches are plugged in correctly (one switch for manual trans cars and two for auto trans cars) and once the throttle is fully engaged, the metal flap pushes in the little plunger on the switch(es) and also releases when it is no longer at full throttle. Confirm the electrical connections are good on the idle speed motor microswitch and it engages adequately when you ease up on the throttle (by way of the lever arm and linkage connected to the throttle spool). We can dial those set pins in more accurately later if need be to get it perfect. Confirm the O2 sensor is connected. Confirm the O2 sensor ground reference wire is making a good connection (it terminates at the block on the passenger side underneath the air filter housing just over from the frequency valve and has a short red wire that connects to the black one that then eventually connects again with the ECU).

Report back anything else you see or notice or remember that isn't stock on your car or that you might already be aware of a problem with. List things you might not have thought of as being relevant to the idle issues since you mention it is having struggles with the A/C on. You could also have some other wonky issue relating to this in a different electrical connection with the A/C, or a vacuum hose that isn't where it should be in the HVAC mode switch, brake booster or who knows where else. Those other areas that might be problematic might not be directly causing engine idling problems, but they might let us figure out what else in common is happening that is the real problem.

[DeLorean937]

I would suggest getting everything hooked-up and connected as intended and then give us a summary of what is happening (pictures, videos or just words). Without knowing the car's history or what else might be going on in the past or present, I don't find the experimentation aspect of disconnecting things and then seeing what happens particularly useful.

Get everything in your engine bay connected as shown in the vacuum routing diagram (vacuum lines and the wiring connections). Confirm all hoses are in place and snug without obvious cracks or leaks. Confirm the electrical connections are all clean, showing bare metal and then snugged in place with the metal clasps holding them so. Confirm all three of those brass screws are threaded in all the way and snug. Confirm your full throttle microswitches are plugged in correctly (one switch for manual trans cars and two for auto trans cars) and once the throttle is fully engaged, the metal flap pushes in the little plunger on the switch(es) and also releases when it is no longer at full throttle. Confirm the electrical connections are good on the idle speed motor microswitch and it engages adequately when you ease up on the throttle (by way of the lever arm and linkage connected to the throttle spool). We can dial those set pins in more accurately later if need be to get it perfect. Confirm the O2 sensor is connected. Confirm the O2 sensor ground reference wire is making a good connection (it terminates at the block on the passenger side underneath the air filter housing just over from the frequency valve and has a short red wire that connects to the black one that then eventually connects again with the ECU).

Report back anything else you see or notice or remember that isn't stock on your car or that you might already be aware of a problem with. List things you might not have thought of as being relevant to the idle issues since you mention it is having struggles with the A/C on. You could also have some other wonky issue relating to this in a different electrical connection with the A/C, or a vacuum hose that isn't where it should be in the HVAC mode switch, brake booster or who knows where else. Those other areas that might be problematic might not be directly causing engine idling problems, but they might let us figure out what else in common is happening that is the real problem.

Ok so to report back.
-I have verified that all hoses are in place and tight. All new silicone vacuum hoses were installed last month.
-All electrical connections including the micro switches and full throttle enrichment switch are plugged and active.
-02 sensor is NOT connected as the car stalls with it connected. It will sure in idle for a while until the exhaust is black then stalls. Always have run it disconnected because of this.
-I have let the system learn as Dave M. has said seems to be a bit better. (Dave is there a better way to set up idle or set up with your RPM system?)
-Now it seems that everything has sort of evened out but now when rev the engine I will get almost a second rev behind it.
-A/C mode switch has been rebuilt and is functioning no leaks there.
-02 sensor wire in connected and grounded.
-Three brass screws and snugged down.
-Frequency Valve is grounded and buzzing loud.


I will cold start the car today and report back the results.

Also on a side note, there is a connection I noticed on the Lambda connector harness looks like a black ground wire that has been cut for some reason. I will post a pic as soon as I can.

[Bitsyncmaster]

The Lambda ECU really needs all three ground wires. Maybe if you hook up that cut ground, you will get it running closed loop.

I run my idle RPM set to 850. You just use the DIP switch to set the idle RPM. I also have the AC "bump" connected so when the AC compressor is on the idle RPM bumps up to 950. I run without the idle switch and also have cut the WOT switch input to the lambda unit because I have a wideband setup with a switch to select richer mixture if I want. My ECU also learns when the AC is running so it keeps two tables within it.

[DeLorean937]

The Lambda ECU really needs all three ground wires. Maybe if you hook up that cut ground, you will get it running closed loop.

I run my idle RPM set to 850. You just use the DIP switch to set the idle RPM. I also have the AC "bump" connected so when the AC compressor is on the idle RPM bumps up to 950. I run without the idle switch and also have cut the WOT switch input to the lambda unit because I have a wideband setup with a switch to select richer mixture if I want. My ECU also learns when the AC is running so it keeps two tables within it.

Ok so I'll set the dip switches to 850 RPM and report back. I will also reconnect the ground on the Lambda harness and see what happens. Also, the AC bump feature is it the blue wire coming from the unit? Just connect it to any 12V source? I have the stock 02 sensor should I still cut the WOT switch input? All in all should I just connect everything from cold start with the system and let it idle until hot so the system can learn? Also the car is an automatic fyi.

[Bitsyncmaster]

Ok so I'll set the dip switches to 850 RPM and report back. I will also reconnect the ground on the Lambda harness and see what happens. Also, the AC bump feature is it the blue wire coming from the unit? Just connect it to any 12V source? I have the stock 02 sensor should I still cut the WOT switch input? All in all should I just connect everything from cold start with the system and let it idle until hot so the system can learn? Also the car is an automatic fyi.

The AC bump wire goes to the pink wire available on a diode in the relay compartment. That pink wire runs to the AC compressor clutch. Yes that is the blue wire from my idle ECU.

You do not cut the WOT wire unless you don't want your WOT to enrich the engine at full throttle.

Yes you need to let it learn so it optimize when your foot comes off the gas. That is the only thing it learns so you can test the idle first and let it learn later if you want. The RPM set change makes those learned tables change a little. It learns when you have a stable idle so the hot engine will learn that temp always. You do the cold start to warm engine idle so it learns all the engine temps even though you may never need those temps optimized.

It should not matter if your car is an auto or manual.