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The car engine also moves up and back when I have it in gear, have my foot of the brake and hit the gas peddle. The car runs great on the open road but when I have to stop in gear it run rough (it shakes a bit). Some have said it needs Transmission/ Engine mounts. Others have said it needs a complete tune up but it starts easily and runs well most of the time.

It's a 1998  Cadillac Deville 4 Door sedan with 4.6 L engine automatic transmission.

1 Answer

by (Genius) (10.4m points)
edited by
0 votes

Hey Frank - Sorry for the delayed reply. Below are things you can try and look at:

  • Try and clean the Idle Air Controller (IAC) valve (Also, the valve could be simply defect and due for replacement on the other hand).
  • Lookup a vacuum leak - this could be your culprit if the rough idle proves to relate much on the brake pedal (when depressing the pedal like at traffic lights as you mentioned). Go as far as the Brake Booster in your vacuum leak quest
  • Also, if you could avail an OBD diagnostic scanner for any stored trouble codes as that would help narrow down the possible causes of the jerking and rough idle issue in question
  • Routinely maintenance including the tranny fluid and cleaning the throttle body and the plate as well may be of help

Let us know how all goes - more emphases on scanning for any stored computer trouble codes.

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