Q: engine hesitation at idle especially when i have the heat or ac on on 2001 Mercury Sable

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ihave a connstant engine hesitation/misfire at idle does not do this while driving but will hesitate real bad if i accelarate to fast.engine light on multiple cyl. misfire codes and bank one lean code. i have already changed the spark plugs twice and also the plug wires.
(1) Answer
(2) Comments
I cannot tell which engine you have, so I am not entirely certain how to respond. However, if you have the 3.0L OHV engine, you could have issues with the valves in your heads. A compression test is in order, perhaps. You could also have injector issues.