Well, for a change, I have a question...
I'm looking at buying a 92 Vette, 95k miles,withan LT-1 (first year available in the Vette). I figured it would be safe to ask here since the engine is pretty much the same as the Camaro, other than factory h.p. rating (300).
In park, it idles fine. When put in drive or reverse, the engine idles a little rough, and makes the car jerk and try to lunge. I can also feel the idle start to speed up a little and make the car creep more. Then when put back in park, the rpm's jump up to 1500, then go backdown right away to around 800-900. I disconnected the Idle Air Control motor, and then it didn't act up. But, is it the IAC, or something else that is controlling it? And what is making the rpm's climb only while in gear?
Another thing it does, is the enginesputters when I rev it in neutral, and if I take off from a standing start, light or heavy gas pedal. And it continues to sputter throughout the upper rpm's. But, I'm thinking that may be a different issue, possibly a needed tune up? No idea if the plugs/wires have ever been changed either. And it sure acts like an ignition problem to me.
The water pump isn't leaking, and the opti-spark is bone dry. The enginedoesn't blow any smoke,black or white. And no SES light either.
I'm curious if anybody else has had these same symptoms, and what was the cure? I've had an LT-1 before in a 96 Z28, but never had these issues. I'm really interested in this Vette, it's a convertiblein decent shape,and only $5,500.

 

Tune up, and IAC are my suggestions.

If that doesn't work, rev the crap out of it, and do an italian tune-up. That's what fixed it for me.

 

My experiences may not directly help you other than to broaden the realm of possibilities. My Z28 ran like crap while my son used it. It turns out he was putting 87 octane gas in it, in spite of the fact that I showed him the manual and pointed out that a P series engine needs 91 octane. The ethanol being put in the gas in my are made matters worse. Once we got the tank back to 91 octane, things were fine.

 

had this problem. for me my iac plug was unplugged. check it

 

Thanks, but if you read my novel (sorry, I had a lot of info to cover) you'll see I unplugged the IAC as a test, and then it did idle better.

 

Sounds to me like the idle problem is probably an issue with the IAC, the sputtering problem I would say plugs, wires, fuel filter, general tune up sorts of things. How many miles are on the car? Even bone dry Optisparks have a tendancy to die around 100,000 miles.

 

It has 95k miles, so yeah the opti is on borrowed time. If the optispark is causing a misfire, wouldn't it throw the SES light on, or not necessarily?
Another possibility that I'm finding is a vacuum leak. Either a vacuum line, or a gasket/seal/o-ring.

 

when i had a vacuum leak, i was at a stop light and it literally tried to lunge forward, it reallt tried to launch hard!

 

I won't always throw a code, so I wouldn't rely on that too much. When I first bought my car cylinder 8 wasn't firing at all due to a fouled plug and there was no SES light, but there was a considerable miss while driving. Sometimes it will throw a random misfire code, but that's usually in the more extreme cases. It's possible the Opti is just on the way out and not to the point of being completely gone.

 

K, thanks. And possibly the less sophisticated OBDI on the '92 might have something to do with no SES?