Hi guys, i'm new here, will write on the 'who is new'pager but first of all, i have a urgent problem with my 93 model C4 with LT1 Engine (Vin P).

The car had some idle troubles, little to high, so i bought a new IAC, and with that, a new throttle body because the old one wasn't nice any more and kind of dirty. Installed the parts but now i have the following problem;
With a cold engine the idle is nice, perfect, at 650 rpm in drive but when the engine gets hotter the rpm gets higher, and when the engine is around 118 degrees Celcius (I'm from Europe so no fahrenheit) the throttle doesn't want to go back, the butterflies stay open and i have to pull the gascable contender back to get to normal idle. Also, when i shut the engine of and start again, the idle is good. BUt hit the throttle once on a hot engine en the butterflies won't go back.. with the engine off the gascable contender can be movede freely and will slam back against the screw but withe the engine on and moving the gascable contender and it won't go back to base position against the screw.

Already did the following;

-adjusted the gascable, now it hangs not really tight, also tried it with the gascable very tight
-IAC installation procedure.
-tried running without the TPS sensor mounted on the throttle body
-tried running without the IAC connected.

None of this mattered.

Thanks in advance from the Netherlands!

by the way,the car is equipped with ASR.

 

Check all vacumme lines

 

Is it possible that vacume can cause this problem? Can a vacume leak only give trouble when the engine is hot? And, is it possible that vacume can hold the Throttle body from getting shut?

 

Anyone? Does anyone knows if the vaume diagrams ar online somewhere? Got 2 tech manuals but both of them dont have the correct diagram...

 

A few questions and suggestions. Are you having the same issues before and after you changed parts? What was a little too high, RPM? Is the throttle blade (butterflies) open the same amount on both throttle bodies? Did you replace with GM parts? did you replace the TPS or transfer from one TB to the other? Once you install the throttle body and adjust the throttle cable you shouldn't mess with it on the throttle body. Did you start it , warm up, then drive at around 40 MPH to reset the IAC? You should check for codes before doing anything else. FYI, a bad TPS can cause a high idle, but it's not the only thing that can.

 

Sorry for reacting kind of late, busy days..


Yes, the idle was kind of high, around 900 RPM with a hot engine.
Did set the IAC, by the installation manual, i drove a straight end for about 10 minutes with 50 mph on the tacho, when i pulled of the highway after that, the problems started, after hitting the throttle the idle wouldn't go back to base and ended at 2500 rpm, when i shut the engine and started it again, the RPM was normal but when i hit the throttle it wouldn't go back from 2500 rpm.


With the old TB the iddle had the same problems, it started after i cleaned the TB and put it back on the car. Changed it for a Summit Power Products TB, a Chevy part is very expensive in Europe with the shipment costs and the taks costs.


I will take the car to the garage on saterday for reading the PCM...


But i think this must be a vacume or other mechanical issue, otherwise the butterflies would go back i pressume... (???)

 

Clean the old throttle body, use correct gasket to bolt up to manifold and install with new IAC of course. Dont rip IAC gasket.
Been through too many throttle bodies on my 93. IAC was always the issue.
iac has no code either, so you can only test it with an ohm meter.