93 suburban wont idle down

[94f450sd]

ok well i just bought this thing.the previous owners fix was to turn the idle screw all the way down till it was about to fall out.SES light flashes randomly.computer has code 35 in it for the IAC motor.at idle the IAC counts are at 0.key on engine off the IAC counts are at 80.i tried 3 different IACs from the junkyard and they all do the same thing.i did get the idle down from 1500 to 1100 RPM.i replaced the throttle body gasket.gonna see if i can check the intake gaskets but wanted to see if anybody had other ideas as well

 

[tonkadoctor]

Test the throttle position sensor, they can cause all kinds off goofy idle and drivability problems.

 

[94f450sd]

tps is fine.supposed to be .50V at idle warm.mine reads .44V.

 

[tonkadoctor]

what else it could be.

If ya want, try a little of this stuff, It'll bring the idle down and you'll never have to worry about fixing the burban again

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[94f450sd]

well it is a GM product. im thinking a leaking intake gasket.i just wanted an easy fix,dont feel like pulling the intake off of it.

 

[tonkadoctor]

You can check for intake gasket and vacuum leaks with a common propane torch.

Remove the torch tip and hook about a 2 or 3 foot section of hose to the torch. Then with the engine running just barely crack the propane open and probe with the hose to see if you find an area where the idle speed increases then goes back down when you remove the propane.

Once you have the general area found you can probe further to try to isolate the cause.

As far as a quick fix for a leaking intake gasket......IMHO there is none, Chebby gaskets don't cost that much and yes it's a bit of a PITA but fix it right and be done with it, bad intake gaskets on a chevy gasser will kill fuel economy but usually produce a rough idle, not a high idle. Seen that with both my Dad's and my brothers burbans very recently.

 

[94f450sd]

i know they are easy and cheap.i used to build chevys till i got into the diesels.i did the carb cleaner trick and the idle changed near the back of the TB so i replaced the gasket for it.its leakin a little oil from the end of the intake so i might as well replace the gaskets anyways and hope i fix 2 problems at the same time