Idle issues

[guss23]

:confused0:Hello all,

I am having some strange idle issues. When starting cold the car starts right up but then idles around 2,000 rpm. After a 4 or 5 min it settles down to 800 rpm then randomly jumps back up to 2,000 and hangs there for a few seconds the bounces back down. I replaced the idle motor, replaced the micro switch, the rpm relay and the fuel computer. What else can it be?

[David T]

:confused0:Hello all,

I am having some strange idle issues. When starting cold the car starts right up but then idles around 2,000 rpm. After a 4 or 5 min it settles down to 800 rpm then randomly jumps back up to 2,000 and hangs there for a few seconds the bounces back down. I replaced the idle motor, replaced the micro switch, the rpm relay and the fuel computer. What else can it be?

Check the quadrant link ends for play and the throttle arm adjustments. Lubricate the throttle cable and throttle spool.

[Jonathan]

When it jumps up, does it go to "around" 2,000 RPM or "exactly" 2,000 RPM?

The reason I ask is because the default idle speed is 2,000 RPM if you were to completely disconnect the white plastic connector on the ECU behind the driver's seat (that module has two connectors on it and the one I mean is on the passenger side of that box).

You can test it easily to see it go to 2,000 RPM by gently disconnecting it while your car is idling in the driveway.

From there you'll see whether it's related to the connections on that box or something else.

If your high idle is 1,800 or 2,100 or 1,400, etc. and you see it come back down after snapping the gas or physically pushing in the throttle spool to contact the idle microswitch, then you know your problem is (likely) in that area (like David mentioned with the adjustments you can look for and try).

There are a metric shit-ton of threads on high idles so spend some time with the search feature and I'm sure you'll find plenty to read about.

[Bitsyncmaster]

When it jumps up, does it go to "around" 2,000 RPM or "exactly" 2,000 RPM?

The reason I ask is because the default idle speed is 2,000 RPM if you were to completely disconnect the white plastic connector on the ECU behind the driver's seat (that module has two connectors on it and the one I mean is on the passenger side of that box).

You can test it easily to see it go to 2,000 RPM by gently disconnecting it while your car is idling in the driveway.

From there you'll see whether it's related to the connections on that box or something else.

That high idle RPM that you get with the idle thermistor disconnected is still dependent on the curb idle setting, engine temp and a few other things. My car would idle around 2500 RPM with the thermistor disconnected (stock idle ECU).

[Jonathan]

That high idle RPM that you get with the idle thermistor disconnected is still dependent on the curb idle setting, engine temp and a few other things. My car would idle around 2500 RPM with the thermistor disconnected (stock idle ECU).

Dave, do you know if there is a difference in the RPM your car will spike to if you A) disconnect just the idle thermistor or B) the entire connector?

I had done the entire connector test a few years ago for different reasons and it would go to exactly 2,000 RPM. This past season though was when I was working on the thermistor problem and that particular test would go to exactly 2,500 RPM.

I may be getting my numbers mixed up though as it seems like a while since I was working on this. I had thought the 2,000 RPM point was some factory default independent of the other settings by virtue of it being a test point.

[Bitsyncmaster]

Dave, do you know if there is a difference in the RPM your car will spike to if you A) disconnect just the idle thermistor or B) the entire connector?

I had done the entire connector test a few years ago for different reasons and it would go to exactly 2,000 RPM. This past season though was when I was working on the thermistor problem and that particular test would go to exactly 2,500 RPM.

I may be getting my numbers mixed up though as it seems like a while since I was working on this. I had thought the 2,000 RPM point was some factory default independent of the other settings by virtue of it being a test point.

I can't really test that anymore because I have my idle ECU installed and don't use the idle switch. But when I did the test on the OEM idle ECU it was disconnecting the thermistor pin only and that went to 2500 RPM. I still would think the RPM will differ dependent on the curb idle setting. I don't think the RPM is closed loop with the thermistor disconnected.

[DMCMW Dave]

Clean/check the wiring connections on the bulkhead connectors. Check the pins on the ISM connector to make sure that they have not pushed out of the shell.

[mluder]

Clean/check the wiring connections on the bulkhead connectors. Check the pins on the ISM connector to make sure that they have not pushed out of the shell.

+1 on this - Also check the ground wire behind the parcel shelf bulkhead. I was having similar issues and it turns out it was loose. Pulled it off cleaned the contact and re-installed. Car runs rock solid now.