If the check engine light is on, First thing you need to do is have the codes read, Autozone does it free, Post the results with the code number(s). Even if the service engine light is not on, there should be freeze frame data stored. If no light You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!
Check the Idle air control valve, it's bolted to the throttlebody, BTW when was the last complete tune up? With this kind of mileage, the fuel pump is also a concern, have the pump pressure tested.
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Thursday, March 13th, 2008 AT 2:44 PM