I have a 1989 GMC Sierra that when the motor is cold it idles up and then will idle down and almost die but not quite and then rev back up. Once it is warmed up it idles fine. I just got it and haven't had a chance to to get it on a portable tach to check if it is idling at proper speed when warmed up any help would be appreciated. God Bless

Have it looked at by a dealer,iam not sure here but i think you have a vacumn leak like the feed pipe to the servo split but really you need a mechanic who works on these cars day in day out and they will go straight too the problem for you

Did you open the hood? It could be a popped serpentine belt or a broken timing chain or timing belt.

the idle control motor probly worn-on the throttlbody--also the tps sensor - get intake area inspectd--a haynes manual will xplain complete car-partstore hazit--------starter fluid is used for low compression or weak spark

See if cleaning the throttle body helps -

TUTORIAL HOW TO clean Vortec Throttle body 5 7L Chevy Gmc

Check the help links related to this problem.Click the link below to go through its troubleshooting procedure :-----Idles rough and quits when gas pedal is pressed less? http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html---------
Car won't start without hitting the gas pedal? http://schematicsdiagram.blogspot.com/2011/12/car-wont-start-without-hitting-gas.html
-------Complete loss of brake pedal then all gets normal? http://repairhelpcenter.blogspot.com/2012/01/complete-loss-of-brake-pedal-then-all.html
------Car dies when gas pedal is pressed? http://schematicsdiagram.blogspot.com/2011/12/car-dies-when-gas-pedal-is-pressed.html
--------Pushing on the gas pedal, but the car slows down? Gas pedal to the floor and the car slows down?

http://technoanswers.blogspot.in/2012/02/pushing-on-gas-pedal-but-car-slows-down.html

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After replacing brake rotors and pads, brake pedal remains on floor? http://technoanswers.blogspot.in/2012/02/after-replacing-brake-rotors-and-pads.html

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accelerator pedal sensor? http://technoanswers.blogspot.in/2012/02/2009-chevy-impala-accelerator-pedal.html

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For rough idle issues and problem troubleshooting,go through the help links provided below :----- van idles rough?

http://howtobyme.blogspot.in/2012/01/2004-ford-freestar-van-idles-rough.html

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will not idle when cold?

http://technoanswers.blogspot.in/2012/02/ford-explorer-40-will-not-idle-when.html

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runs lean and idles rough?

http://technoanswers.blogspot.in/2012/02/ford-runs-lean-and-idles-rough.html

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Engine stumbles coming off idle when warm?

http://repairhelpcenter.blogspot.com/2012/01/engine-stumbles-coming-off-idle-when.html

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Erratic idle on car?

http://schematicsdiagram.blogspot.com/2011/12/erratic-idle-on-car.html

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Low idle when cold out side?

http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html

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Idle Air Control (IAC) Valve Replacing?

http://schematicsdiagram.blogspot.com/2011/12/gmc-idle-air-control-iac-valve.html

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Engine quits at idle?

http://repairhelpcenter.blogspot.com/2011/10/engine-quits-at-idle.html

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Car overheats and Air blows hot at idle?

http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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This will help.

Thanks.

throttle position sensor

if u own a 1989 sierra u dont have an obd or obd ll computer on board if high idle all time then search for a possible vacuum leak and or throttle/carb needs adjustment

This is a safety feature for the motor. It is called a rev limiter. This is meant to prevent the motor from reving at high rpms when at idle. This is completely normal

Check for vacuum hose leaks or component clogs. You can use vacuum pressure tester.
or turn the idle screw down.

idle my be offset or a hose my be off as well