Intermittent high idle

[grubyuppie]

My 93 inline 5 MT EV has a stange high idle pattern.

When the engine is cold it idles around 1300 (good) but then it will idle at 2000 (not good) after reaching normal operating temperature. After a few miles of idling high it then drops down to a normal idle (good.)

No codes on the Ross Tech. No other issues.

[gti_matt]

1300 cold is still a bit high.

I would make sure the ignition timing is correct, no vacuum leaks, make sure the idle stabilizer valve is working (with engine off and ignition on it should vibrate slightly; you can feel it with your hand), clean the ISV, and clean the throttle body. Then, assuming the ECU's coolant sensor is working within spec, reset the ECU.

ECU reset:

1. Drive van until fully warm, best if cooling fans cycle on/off at least once.

2. Stop engine.

3. Disconnect coolant sensor for ECU at the 2-pin connector and disconnect and plug PCV valve hose atop the valve cover. Make sure that all lights and climate controls are completely off.

4. Start van, let it idle for at least one minute.

5. Stop engine, reconnect coolant sensor and PCV hose (but if fans come on, wait until they shut off before connecting coolant sensor; connecting while they're running will fry the ECU).

[grubyuppie]

Thanks for the help on this project. I fixed the idle problem without resetting the ECU. I found a small vacuum line that I didn't replace when I installed all new lines on the engine. That fixed it!

[gti_matt]

Thanks for the help on this project. I fixed the idle problem without resetting the ECU. I found a small vacuum line that I didn't replace when I installed all new lines on the engine. That fixed it!

Should idle in neutral at about 750-800. I found on mine that after sorting all its issues (proactively replaced all the little vacuum lines), had the throttle body cleaned, and replaced the ECU temp sensor proactively, did the reset procedure, and it idled warm with the tach pointer just a hair below the tick mark that is before 1000 rpm. So from 1000 rpm, go one tick mark down from that, and then the tach pointer was just below that. All that, plus new engine mounts all around, and the van is a nice and smooth idler with very little noise.

[grubyuppie]

Should idle in neutral at about 750-800. I found on mine that after sorting all its issues (proactively replaced all the little vacuum lines), had the throttle body cleaned, and replaced the ECU temp sensor proactively, did the reset procedure, and it idled warm with the tach pointer just a hair below the tick mark that is before 1000 rpm. So from 1000 rpm, go one tick mark down from that, and then the tach pointer was just below that. All that, plus new engine mounts all around, and the van is a nice and smooth idler with very little noise.

Matt,
Where is the ECU temp sensor?
Also, how difficult is the job to replace all of the engine/tranny mounts?

[gti_matt]

The ECU's temperature sensor is in a plastic neck coming out of the head (between cylinders 2 and 3 I believe). It's the 2-wire sensor.

The motor mounts aren't that bad to replace although I had a shop do the rear one because it was too tight and I was having a hard time getting the bolts undone. But for the upper ones on the sides, they're pretty easy.

I placed the car's jack (with a 2x4 in the saddle as a buffer so no metal-to-metal contact) under the engine/trans. When working on the trans side one, I placed it where the bellhousing and motor meet. When working on the passenger side one, I placed it where the accessory bracket bolts to the engine. You don't have to lift the engine much but the idea is to get some support under it to control it when the mount isn't there. Do one side at a time. Undo the three bolts up top, lower engine/trans slightly for clearance, pull mount out, slide new mount in, jack up into place, tighten to spec (with some upward pressure on the jack so the bolts are not yet taking the weight while you torque them down). Repeat for other side.