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High Idle Issue


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It hit 70 in the great northwest today...so time for a top-down cruise!

The car hadn't been started for a few weeks, but started promptly (like usual). However, the car went to an idle speed of 2500 and stayed there for the first 3 plus miles. Then the idle speed went to around 1500 and stayed there for the next couple of miles. We stopped at our destination, and the car sat for 30 minutes, then restarted with normal idle speed. Any ideas on what is going on?

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I will offer this: I have an 88 and '98 Olds with 3800s. The other day I started the '98 and it would not idle, started and died several times. I held the accelerator pedal down a little and cranked it up, ran ok until I released the pedal and it died. I raised the hood and pecked on the idle speed control solenoid and tried again, it cranked right up and ran fine.

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Could be your IAC stuck and took some time to correct itself. In which case pulling it and cleaning it per the instructions on Ronnie's site would serve you well.

Could be you have a vacuum leak that heals itself as the engine temp rises. If so I would expect it would recur next time you drive until you can ferret it out.

Could be one of the values of the ECM's block learning parameters in memory hiccuped and needed to reset itself to a more proper level. This will not recur unless you don't have good voltage being maintained to the computers from bad connections at the battery or the ground terminals.

Or it could just be your car was in a state of shock from the good weather. Kind of like Punxsutawney Phil seeing his shadow. This shouldn't recur for another year or so.

Could always use diagnostics to look at the ECM data and see if anything is out of wack.

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I have similar issues. I did have a bad throttle position sensor, but every once in a while the engine still tachs up to around 2500 rpm. If I shut off the engine and restart it immediately, it returns to normal. I've been told a faulty coolant temp sensor could cause the high idle, but I have yet to look at those values (ED04) when the problem occurs.

So many things could cause this problem, but checking your ecm info is the best place to begin.

We had a beautiful weekend here in the midwest-77 degrees--the Reatta saw about 700 miles of country roads.

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i had a similar issue on my CTS V-6 on a trip to Raleigh this past Saturday. weird high idles - but mainly dying at stop lights. then sputters at speed. the check engine light came on. i had to "heel & toe" it taking off at stoplights. long story short - it turned out to be a badly cracked vacuum hose from the intake to the engine that had let go from the intake. i replaced the rubber and all is well.

just something to check before purchasing a new MAF or IAC, etc...:)

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Thanks Gents! This is a good list to work on. The problem re-occurred on the second of two 70 degree days. The IAC is relatively new, so I suspect a vacuum leak.

It's time to do some "bonding" with the engine compartment, or seek professional help (for the car...that is, although I could probably use it too!)

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Gary,

Is your car showing a Vehicle Speed Sensor (VSS) code? It is EO24. After the car is started after being shut down for a time, the idle is very high. The only way to get it down in the normal range is to clear the code. Just as soon as the code is cleared the idle drops down. It stays normal until the next time it is restarted.

Not to say that this is your problem but, someone searching the Forum might find this useful.

John F.

Edited by Machiner 55
Added, Not to say... (see edit history)
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  • 5 months later...

Sorry for "slacking" and not posting the final chapter on this issue sooner...

My auto care provider diagnosed the schizophrenic high idle as a faulty ECM. After replacement with a Delco re-manufactured unit the issue was cured!

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