Question
Why does my car idle rough when AC is on?
The rough idle is mostly due to the extra load the air conditioning system puts on the engine. Common causes for the problem include a dirty throttle body, faulty idle air control (IAC) valve, vacuum leaks, or a stuck EGR valve.
It is a common issue, particularly in older vehicles. Once the AC clutch is engaged, it puts additional strain on the engine. Moreover, if there are any underlying problems, the engine may struggle to maintain a steady idle. Cleaning the throttle body, checking for leaks, or servicing the IAC valve often helps fix the problem.
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