High idle when cold

[Kevin]

Hi all,

Sorry for yet another high idle thread, but I haven't been able to find this symptom in the archives.

This just started out of the blue today. When the engine is cold, it idles around 2000 RPM. After it finally warms up, it idles like normal.

I just checked my thermistor, it's at around 1100 ohms with the engine hot enough to turn down the idle. Throttle linkage seems good, rocker arm is seated fine and microswitch is engaged, throttle spool returns to resting position.

Given all this, what else should I be checking for a temperature-sensitive idle?

Thanks!

[Bitsyncmaster]

Strange problem. My first check would be to try another idle ECU. You can short circuit those sensor wires as another check.

[Rich]

You didn't make any vacuum hose checks recently?

Truly an out of the blue problem?

Might be the ECU, as Dave says.

Or the idle control motor may be sticking or not well-connected. It starts out wide open (high idle) and is supposed to go into speed-control mode (in a restrictive control range) immediately after starting.

A crude check would be to rap lightly on the side of the idle control motor next time you get a high idle and see what happens. Beyond that you'd need to take it off and clean it.

[Kevin]

Strange problem. My first check would be to try another idle ECU. You can short circuit those sensor wires as another check.

Wish I had another ECU! I'll check the sensor again once it cools down and maybe jump the connector pins then too.


You can start with the simplest test which is to verify that the throttle is fully closed when the car is idling cold or hot.

Find the end of the throttle linkage. When you encounter a high-idle condition then push on the upper end of the linkage.

In all idle situations it should already be closed. If it is indeed fully closed and still runs 2000RPM then we look elsewhere.

That's one of the first things I did. I pressed on the throttle arm to make sure it was all the way down and made sure the throttle spool wasn't stuck or engaged in anyway. I also backed out the curb idle screw to make the arm go down even more and the idle went down some but then went right back up again.

[Rich]

Things got out of order there, meant to retract the linkage q.

The idle control motor may be sticking or not well-connected. It normally starts out wide open (high idle) and is supposed to go into speed-control mode (in a restrictive control range) immediately after starting. Maybe yours isn't - til it's warm?

Try rapping lightly on the side of the idle control motor next time you get a high idle to see if that coaxes it into action. Even if it doesn't the idle motor may still be a cause.

[DeLorean03]

Wish I had another ECU! I'll check the sensor again once it cools down and maybe jump the connector pins then too.







I have a spare I would be willing to sell.... : )

[Michael]

Make sure the idle switch has not had a wire come off.

[hmcelraft]

Have you checked the vacuum lines at the Fuel Control Pressure regulator? Also, the function of the Thermally controlled vacuum switch?

[Kevin]

Yes, vacuum lines look good. Yes, the wires are still attached to the microswitch. No I haven't checked the operation of the thermo vac switch.

But, I went to start it this afternoon after it had been sitting overnight and it idled perfectly. This makes me think Rich's theory about the idle motor could be sticking or not well-connected since it's not consistent. We'll see if it happens again and I'll tap on the motor. If it is sticking, is it a sign the motor is about to go?

I appreciate for your feedback, everyone!

[DMCMW Dave]

Yes, vacuum lines look good. Yes, the wires are still attached to the microswitch. No I haven't checked the operation of the thermo vac switch.

But, I went to start it this afternoon after it had been sitting overnight and it idled perfectly. This makes me think Rich's theory about the idle motor could be sticking or not well-connected since it's not consistent. We'll see if it happens again and I'll tap on the motor. If it is sticking, is it a sign the motor is about to go?

I appreciate for your feedback, everyone!


Pull the wire off the motor and inspect the terminals. If they are green or pushed back take appropriate action.

[Kevin]

Pull the wire off the motor and inspect the terminals. If they are green or pushed back take appropriate action.

Good thinkin'. Just did that and the connector terminals have a little bit of green on them, could be our problem!

Thanks again, all, I'll continue my focus on the idle motor and connector if this happens again.