Without understanding the type of noise, it is not possible to provide any insight into the problem. It could be idler or alternator bearings ( coarse noise ), ticking noise ( engine mechanical or vlave lifters), screeching ( loose beltings ) etc.
If you are able to provide a clear description of the noise and its occurrence conditions, for me to understand the problem I might be able to provide some suggestions.
As to the erratic idling when stopping, it most probably is due to clogging of the intake passages.
When dirt builds up in the throttle body and Idle Air control valve,, it would restrict the amount of air getting into the intake manifold. When this occurs, the PCM would try to correct the idling, thus the erratic idling. The idling would drop and try to catch as the PCM readjustes itself.
The air passages needs to be cleaned to enable proper air flow and the easiest way to do it is to get a can of carb cleaner to spray into the throttle body and IAC to clear out the dirt accumulation.
Use a piece to scrub the inner port of the throttle body to save time.
This link explains the process in more details though it is for a Honda. Your vehicle is equipped with a MAF so the last part is not applicable as you need to reinstall the air cleaner hose before the engine can run properly.
By the way, check the hose between air cleaner and throttle body for cracks which would allow vacumn leakages and cause erratic idling.
Tuesday, February 16th, 2010 AT 2:31 AM