Rought and low idle at stop [Archive] - GrandAmGT.com Forum

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Rb737
02-22-2010, 03:50 AM
when i am at a stop or in park, my car idles pretty rough, and about 100rpm below normal. i have changed the plugs an wires, cleaned the IAC valce, cleaned the Throttle body, Cleaned the Throttle positioning sensor, changed most of the vaccume hoses and inspected others,ive done a torque test for the motor mounts, ive tested the fuel pressure regulator, and changed the fuel filter, brand new battery, ive done practically everything i can think of and the problem still hasnt gone away, i have 85k miles and no service lights or weird sounds...car runs smoothly when driving, smooth shifting etc.....im a little lost on how to find this problem, any help or advice is greatly appreciated, thank you.

PhantomLover007
02-22-2010, 02:22 PM
Cloggeed cat?

Rb737
02-22-2010, 07:43 PM
im not getting any weird smells, doesnt the cat usually let off a rotten egg smell when its clogged?

AaronGTR
02-22-2010, 08:05 PM
Not necessarily. It could also be a dirty MAF sensor or a failing O2 sensor. Both of those can make the car idle rough and won't necessarily throw codes until they get really bad or fail out right. Cleaning the MAF is one of the first things we usually recommend.

Rb737
02-23-2010, 02:09 AM
the car has 86k miles on it and the 02 sensors have never been changed, how can i test those?

Rb737
02-23-2010, 02:11 AM
also, when i turn my wheel all the way to the right or left when in park, my rpm drops about 150rpm to about 500 and then jumps back up to 650 and bobbles a little...is that a sign of a bad iac valve? or maybe a dieing alternator?

AaronGTR
02-23-2010, 04:45 PM
the car has 86k miles on it and the 02 sensors have never been changed, how can i test those?

There's not an easy way to test them. If you had a scanner and a wideband O2 sensor you could compare the narrow band activity to what the wideband is reading. Usually though you can't tell they are bad until the switching gets slow enough that the computer sets a code, or if you replace the sensor and see an improvement. They usually recommend replacing the sensors at least by 100k miles, so I'd say you are close enough to the change point that they might be starting to go. New sensors can improve your gas mileage and idle too, so it might be worth doing. It's your choice.

also, when i turn my wheel all the way to the right or left when in park, my rpm drops about 150rpm to about 500 and then jumps back up to 650 and bobbles a little...is that a sign of a bad iac valve? or maybe a dieing alternator?

Sounds like typical drag from the power steering pump. When you lock out the wheel left or right and are still trying to turn the steering wheel, it puts a lot of extra load on the pump and can slow down the engine.

Rb737
02-26-2010, 06:06 PM
so what do you think is my best bet...its a noticeably rough idle and low rpm at stop...but no service lights...i wanna start replacing things from least expensive possible to most expensive possible....should i test the fuel pressure? maybe replace the IAC or throttle positioning sensor? do u think the tensionor could be a little loose? where do u think i should start to fix this little problem. thank you for your help