Extremely high idle??! help?

Thatlowchevy · Oct 1, 2016

I just got rid of my 1995 Silverado for a 1991 Chevy K2500 and its been running great! besides the weak reverse nothing has been wrong. yesterday we cut off the stock muffler and put on a Flowmaster which sounds amazing BTW, now it has an idle around 2000 RPM and its really killing the tranny, i let off the brake at a stop light and it spins tires. i replaced the CTS (Coolant Temp Sensor) and it finally went down to around 900 rpm, then i shut it off thinking it was good and it shot back up to 2000... ive rebuilt plenty of TBI engines and this is the first that has actually stumped me like this. any insight will be appreciated. thanks again!

98sierraslt4x4 · Oct 1, 2016

"Any time there is a high idle on a TBI or other fuel injection setup, there is too much air getting into the motor.

This vacuum leak can be at the IAC valve. IAC valve is a regulated vacuum leak, controlled by the ECM. If it is stuck open, it is a larger than necessary vacuum leak.

If the intake gaskets, base plate gaskets, or vacuum lines are leaking (like the PCV valve), or the brake booster - then it is introducing air into the motor it shouldn't be - which is a vacuum leak.

All high idles are a vacuum leak of some kind. " cut and pasted from here. But they never followed up to say if i was a vacuum leak or not...

Fast Idle Problem 95 K1500 - ChevyTalk - FREE Restoration and Repair Help for your Chevrolet
http://www.chevytalk.org/fusionbb/showtopic.php?tid/287132/

Thatlowchevy · Oct 1, 2016

thank you for your info, but i found something out. with the engine running you can press the EGR diaphragm and the idle will go down until it is almost a dead stop. could this be my problem?

98sierraslt4x4 said:
"Any time there is a high idle on a TBI or other fuel injection setup, there is too much air getting into the motor.

This vacuum leak can be at the IAC valve. IAC valve is a regulated vacuum leak, controlled by the ECM. If it is stuck open, it is a larger than necessary vacuum leak.

If the intake gaskets, base plate gaskets, or vacuum lines are leaking (like the PCV valve), or the brake booster - then it is introducing air into the motor it shouldn't be - which is a vacuum leak.

All high idles are a vacuum leak of some kind. " cut and pasted from here. But they never followed up to say if i was a vacuum leak or not...

Fast Idle Problem 95 K1500 - ChevyTalk - FREE Restoration and Repair Help for your Chevrolet
http://www.chevytalk.org/fusionbb/showtopic.php?tid/287132/

Thatlowchevy · Oct 3, 2016

Figured out what it was!!! the TPS as well as the CTS went out at the same time and were intermittently causing problems.

98sierraslt4x4 · Oct 4, 2016

Thatlow95 said:
Figured out what it was!!! the TPS as well as the CTS went out at the same time and were intermittently causing problems.

Nice. I'm surprised the ECM didn't throw a code from that tps not communicating correctly.

wheelman · Oct 4, 2016

if you have not changed that TBI BASE GASKET -better change it -they go bad and leak air-with engine running.spray something on the right side of the throttle body..see if it idles up or down..

Extremely high idle??! help?

Thatlowchevy

How’d I get inside this tube?!?!

98sierraslt4x4

OBS Enthusiast

Thatlowchevy

How’d I get inside this tube?!?!

Thatlowchevy

How’d I get inside this tube?!?!

98sierraslt4x4

OBS Enthusiast

wheelman

I'm Awesome

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