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rough idle in N or D


Henri 79

Hello all,

I already did a search in the database for rough idle but somehow I cannot relate the found symptoms to mine.

I have a '91 Vette auto, with 39000 miles on it. It's a decent driver in excellent shape, never had any problems. Runs great, idles very nice, dyno tests showed it has all the hp & torque GM promised me :)

But since yesterday I noticed a strange thing: while driving and getting off the go pedal, the rpm's dropped more than I'm used to. Around 1000 rpm, going an 50 km/h (30 mph). Funny thing is that I don't remember what the rpm used to be at these speeds while going off the gas pedal, but definitely higher.

And while on idle, the rpm's fluctuate way below what I'm used to see. Normally it idles around 900 rpm, but now it's below and not constant. I even noticed an almost 'die', but then it came back.

The very funny thing is that both symptoms come and go. Sometimes it runs like it used to, and sometimes there is that strange behaviour.

What to do? Please remember I live in the Netherlands and Corvette expertise is very hard to find. Would love to try the easy things myself first.

Read a lot about the IAC. What is that? Where is it?

Thanks in advance!




On my 84 I found idle problems came from 2 sources. First was the Throttle Position Sensor (TPS). I reset it for .525 volts and that helped alot.

The second thibg was the EGR valve. I was getting a little bit of leakage when it was suposed to be closed. I made an alumimnum block of plate to fit under it. Smothed out the Idle real nice.

Hope this helps.


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