High idle on 5.7L Vortec

RKBJR

RKBJR

Well-Known Member
Joined
Mar 21, 2005
Location
Roxboro, NC
I'm getting a high idle on the Vortec 350 in my Cruiser. It idles like it should when the engine is cold. Once it warms up to normal operating temperature, it revs higher at idle. Anyone have this problem before?

R.K.
 
More than likely a vacuum leak. intake gaskets are a common failure on those engines. could be a vacuum line of fitting cracked.

spray it down with brake or carb cleaner (use the straw o the spray nozzle) following intake at head, around the thottle body and anything else that might could leak air.
 
I just had the intake gaskets replaced. I had the high idle problem before and after having them replaced.
 
It could very well be the computer.. If you're gonna run some whiz-bang high-tech motor like that, you'd be very good to have a tool that can monitor the sensors and ECU output real-time for diagnosis. :flipoff2:

There's a ton of things that could make the idle high.. and a BUNCH of sensors.. Off the top of my head - thinks A/C is engaged, thinks it's constantly cold, etc..
 
do you have an OBD2 connector on your harness?...the guy who did mine for the LS1 left the OBD2 connector on it and I can still monitor all the engine stuff, all you would need is a cheap scanner.
 
We fixed one small vacuum leak, but that wasn't the problem. The throttle cable was tighter than it should be. We modified the bracket to give it some slack, but it still idles a little high when warm. It has a slight surge, almost like it wants to idle back down, but then kicks up again. When I turn the engine off, and then back on, it idles fine. I do have a diagnostic port on the Painless harness, so I will try to pull some codes tomorrow.

R.K.
 
Try taking off your air induction, and look on the inside of the throttle body. There should be a little hole off to the side, spray that hole with Throttle and choke cleaner and spray your throttle body down real good. Some times cabon builds up in there and make the Throttle position sensor act funny.-David
 
R.K. , It's most likely the coolant temperature sensor (not sender) for the computer if it is not a vacuum leak. Very common problem for the SBC F.I. swap that sees some engine washing occasionally. Mine went bad at tellico at the dixie last year, the idle will eventually keep creeping up until its too high to drive with.

Hope It Helps, Greg
 
Replaced the coolant temperature sensor today, seems to have helped some. But it still idles higher than it should.

Gonna clean out the throttle body next. Any other suggestions?
 
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