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high and low idle on 5.3

high and low idle on 5.3

Postby booger [OP] » Feb 15 2013, 7:55pm

i have a 2000 gmc with 275,000 miles on it. recently it started to idle high (1200 rpm) after i drive it a while. if i shut it off at the stop light for about 20 seconds it starts up and idles fine for the next few miles. it comes and goes. it stopped for a few months now its back.
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Re: high and low idle on 5.3

Postby booger [OP] » Feb 17 2013, 6:17pm

now i unplugged the throttle position sensor and it goes down to normal idle. what sensor would tell it to do that.
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high and low idle on 5.3

Postby Machster69 » Feb 17 2013, 6:58pm

What actions preceded this behavior?
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Re: high and low idle on 5.3

Postby KrisK » Feb 17 2013, 8:02pm

Is the truck showing any codes, your check engine light on? Did you check your intake from your air filter to your throttle body for any cracks or leaks? Check all you vac lines for damage? Throttle body clean?
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Re: high and low idle on 5.3

Postby booger [OP] » Feb 17 2013, 9:49pm

yeah, the intake and such are clean and air tight. it only does it after i drive a few miles. if i unplug the throttle position sensor it will idle at 550 rpm. no engine codes show up. could a bad speed sensor do it.
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Re: high and low idle on 5.3

Postby KrisK » Feb 17 2013, 10:13pm

I wouldn't think it is a speed sensor, that's more having issues with transmission, speedometer, ABS, power steering ( I could be wrong ). Did you check your MAF for any obstructions? Maybe a temperature sensor problem. Engine might think its still cold and running higher rpm to worm up? I am just speculating though. Might pay off to take to a shop when the problem occurs and have them diagnose while running. Looks like you have checked most of the common things I can think of. Maybe others can point out something I have missed. Good Luck.
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Re: high and low idle on 5.3

Postby booger [OP] » Feb 17 2013, 11:48pm

well its fixed, i just took out the idle air control valve. it didnt look too dirty, but hit it with carb cleaner, pulled the plunger in and out and put it back in. at first it idled at 2000 rpm, highest yet, so i thought i found the problem. drove it to the parts store to get another one. i shut it off, still idling at 2000. when i came out everything is normal. drove it for 20 miles, still fine. knock on wood.....
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