Could be dozens of things. Fuel supply problem, sensor problem, Engine Computer problem. The place to start is by reading any stored diagnostic fault codes. If the computer detects a problem that could adversely affect tail pipe emissions, it will turn on the Check Engine light, but there can be other codes in memory that do not cause the light to be on.
If there are no codes stored in memory, your mechanic can use the same hand-held computer, called a scanner, to watch various sensor readings when the problem occurs. If it happens too quicky, they have a "record / playback" function that will record a few seconds of sensor readings. They press the "record" button when the problem occurs, and the scanner actually starts recording from its memory a few seconds before the button was pressed. Later, the series of events can be played back and scrutinized for clues.
Friday, March 12th, 2010 AT 2:10 PM