what would cause my car to missfire on all 4 cylinders? i changed the cap rotor spark plugs wires.. and its still doing it?? it only does it at idle... when i hold the rpm at a steady pace it doesnt missfire.. only at idle... can someone help..

 

Sometimes a rough running engine at idle, yet sounds healthy when revved can be caused by the EGR valve sticking open. It recirculates too much gas at too low an engine speed for the motor to burn it off properly, cause a rough idle.