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95 Olds Cutlass fast/high Idle speed

A

Anonymous-0

Well-known Member
Wifes car idles around 1100 rpms and faster at times. I replaced the head gaskets a few years ago so the intakes should be fine. I have sprayed carb brake clean around the intake trying to find a leak. And have tried propane around the intake for another test. Also replaced the idle air control motor, and tried a different pcm from another car. Had a friend put the scanner on the car and all the values were good. When we first noticed this I found the breather tubes from the rocker arm covers were leaking around the grommets so replaced grommets and tubes. Any suggestions thanks chris
 
It may be the throttle position sensor. I had a S-10 Chevy that done the same thing and after replacing the sensor, all was good
 
Fought with my 95 buick all summer, exact same thing, changed the throttle position sensor, cured all problems, it hasn't run this nice for a long time!!
 
If it were me, I would take a can of ether and start with small bursts around the firewall untill you hear the engine slightly race as you spray. As the ether meets the vacuum leak it will be drawn into the intake manifold and make the engine race slightly. When you find the area that the leak is, try pin pointing which sensor is leaking. Once you find the area where the leak is, you can start looking for hoses that aren"t attached and sensors that don"t have their hose attached etc.
 
Did he check the idle air control (IAC) motor steps? If it is zero or close it's a vacuum leak; if it's in the teens it may be a defective IAC motor.
 
yepper ,look at IAC counts before you go spraying stuff all over searching for a vac leak thats not there . If counts are up ,,you need to look at PCM inputs ,,,power steering pressure switch , a/c switch , park neutral switch . Any of these can cause IAC to raise idle speed
 
Check the wiring first, one is ground, if you unplug it you should get a low code, if you jumper it you should get a high reading code and a check engine light. Last spring I had a engine light on a 95 buick, tps code, was running kind of crappy, changed tps and thats when I started having high idle problems, just setting there would speed up to 1500 all by its self, shut it off and restart and it would be good, changed the air idle controller, didn't help a bit. Messed with it all summer, talked to a friend at GM said throw that CarQuest tps away and put a GM one on, I thought ya-right. He WAS right, the Car Quest part was no good,new GM one and all problems gone, car hasn't run this nice in a long time!! Messed with that darn thing for 4 months.
 
Last night while putting in the original pcm I heard a humming noise like the fuel pump cycling. I noticed this over the weekend with the second pcm also just walking by. Happens like 3-4 minutes apart. Ignition off. Would it hurt to check the fuel pressure, would high fuel pressure cause high/fast idle. thanks guys
 
Try a new thermostat; may be partially stuck open. I have seen several FI engines do this and they were not coming up to operating temperature. ECM thinks they are cold all the time and call for a faster idle.
 
I did check the wiring like you said and everything checked out. I did replace the IAC motor with a GM one.
 
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