I have a problem with my car. I have brought it in for service, but they could not find the problem much to my frustration. When I start the car in the morning, particularly when it has been cold for a long period of time like in the morning, the car starts up very loudly and it idles rough. It drives fine (although it is still loud) but when I come to a stop and it is idling, it again idles rough. When I drive the car for 15-20 minutes, the car idles perfectly. As the mornings get colder, the idling and sound is getting worse. My mechanic could not diagnose the problem. I don’t know what to do at this point since the problem seems to be getting worse. The car is a Ford Focus 2001.
Some maybes:
faulty IAC valve (I like this one)
Dirty throttle body
Faulty MAF sensor (Mass Air Flow)