My 94 Z/28 has a LT1 350, 79000 miles on it. After it get up to operating temps it will rev up to 2000rpm when sitting at a traffic light or stop sign. I have had it to several Chevy Stores and no one can find what is causing this problem. I had the throttle body cleaned out and have ran several cans of Sea Foam with no results, same problem. I know it needs new plugs and wires which I will put on this winter, but what the H**l is causing the reving up problem? Anybody else have the same problem?

 

Maybe not the exact same, but I have an idling issue. We've checked almost everything from vacuum lines to sensors and the iac valve with no luck. I believe I'm still picking up air from somewhere(vacuum leak) which is causing the high idle. All me sensor volts are within spec and I'm lost as to what it could be.

So try checking the vacuum lines for leaks and go over your iac valve and tps one more time to rule them out for sure.

 

Agreed. Any vacuum leak will cause the motor to rev. But the only flag thrown in my head with this theory is why is it only when it is warm? This leads me to believe it may be iac valve, possibly an o2 sensor.

To further diagnose the problem we need to know about your car. Try setting up a signature with year and any mods of your car.

 

The map sensor is often overlooked. It has a rubber seal that can go bad or leak.

 

My friend bought a 94 z28 that does this. misses alot, sometimes idles up to 2000rpm, failed smog test (super high HC and NOX) no service engine light has come on. It is also very hard to start at times .... sorry for hijacking anyone have a clue on this? Also has a K & N cold air setup on it but has some weird vacuum line plugged into the intake elbow with what looks like a 1 way check valve.

 

Try taking the vac line off of your EGR valve and plugging it, see how it runs after that. Mine did the same thing. Good luck

 

or just delete the egr valve as a whole.