Passenger side LH, under bonnet.

I would first query you as to whether the vehicle had a recent battery replacement or if the battery was disconnected during the performance of some other service being done? If so when the battery is reconnected the throttle assy. resets the throttle blade to the preset position desired by the ECM programming but assumes the throttle bore and throttle plate to be free of contamination. Throttle bodies require periodic maintenance due to a condition called COKING if the throttle plate was all choked with carbon then the throttle body should be properly cleaned and an IDLE RELEARN performed. The other issue that is a factor in the standard shift model is a defective neutral switch which signals the PCM at both acceleration and deceleration to either request idle state to be engaged or to be disengaged electrically during shifting and cruise. Hope this sheds a little light on your issue! Kagan's Service Station Inc. Brian Kagan