Extremely High Idle Spped - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 08-08-2010, 02:05 AM   #1
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Default Extremely High Idle Spped

Recently, my '97 Bonneville has been running extremely fast on starting--close to 2500 RPM. This continues even after the engine has reached operating temperature. After driving for a few miles and coming to a stop, the RPM with the engine in gear and at a full stop still runs at over 1500, and then gradually decreases to a more normal 900 if a sit at a stop for a few seconds. Could this be a PCM issue?
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Old 08-08-2010, 02:54 AM   #2
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sounds like a possible TPS issue...

do you have any warning lights on your dash? and is there a way you could scan the car for codes?

ps if you dont have a scanner..autozone will scan your car for free for codes
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Old 08-08-2010, 02:55 AM   #3
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Quote:
Originally Posted by lonestardave View Post
Recently, my '97 Bonneville has been running extremely fast on starting--close to 2500 RPM. This continues even after the engine has reached operating temperature. After driving for a few miles and coming to a stop, the RPM with the engine in gear and at a full stop still runs at over 1500, and then gradually decreases to a more normal 900 if a sit at a stop for a few seconds. Could this be a PCM issue?
Check your engine bay for broken or loose vacuum hoses, or for any vacuum leaks. This would certainly cause an unusually high idle. Is it throwing any codes?

This problem could be related to the throttle position sensor, though I can't say for sure.
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Old 08-08-2010, 12:51 PM   #4
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Sounds like the same issue I had a few months ago, Id use Danthurs testing procedure for Throttle position sensor in the tech section of the forum. Also check your Idle air control sensor. Mine turned out to be iac was gunked up so, I replaced both sensors and cured the problem.
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Old 08-08-2010, 01:29 PM   #5
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First thing you want to do is make sure the throttle is returning to closed. Watch the cables for any binding. If it reutnrs to closed then take the throttle body off and clean it, I'm guessing it'* all gunked up. Testing the TPS is a good idea.
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Old 08-08-2010, 02:02 PM   #6
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my car did this when my exhaust broke off my 1993 SE. the car would idle high and would accelerate without hitting the gas, all the way up to 55 mph or so. lol
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Old 08-09-2010, 12:38 AM   #7
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Thanks for all the suggestions. There are no warning lights on, and it'* not throwing any codes. Tomorrow'* my day off, so I'll check out all the sensors, etc., and see what turns up.
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Old 08-09-2010, 07:28 AM   #8
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I'm right there with the others. My steps would be to check for binding throttle at the same time as listening in for vacuum leaks. That'* a huge leak if it'* a broken hose. Almost brake booster in size.

Then I'd move on to throttle body and IAC cleaning. After that I'd hit up the TPS check. (Unless you have a scanner, then I'd TPS before doing any dirty work. )
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Old 08-09-2010, 11:54 PM   #9
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The throttle body was filthy andthe TPS was bad. Throttle body cleaned, TPS replaced, problem gone. Muchas gracias.
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Old 08-10-2010, 07:44 AM   #10
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De nada Senior
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