I just got my car back yesterday from my new mechanic in the Oceanside area. I brought the car in under the guise of an unstable idle (minor) with no trouble codes; and RPMs diving down to 650 when coming to a complete stop causing a near stall situation. Here is what he did:
His scan showed that the actual and desired minimum throttle PIDs did not match and found that the minimum throttle setting was not complete (ie: apparently whenever the battery is removed, a throttle relearn procedure is supposed to be performed). He removed the throttle bore assembly and cleaned the throttle plates with a tooth brush and Amsoil (Seafoam equivalent). He performed the throttle relearn procedure using the scan tool and identified that the PIDs are at the correct setting.
http://diycardoctor.com/accelerator_pedal_position.htm
He also said that my rear engine mount may be weakening internally, although it was at the proper level. He also said that I should wait for a code on my ignition coils and not waste money putting new ones in as preventative maintenance.
This guy seemed real sharp; much better than my old mechanic back in DC. With a lot of carbon removed using the Amsoil ("Seafoam") product, the car still dives down to 650 at a hard stop, but recovers much quicker and does not shudder as if it is about to stall.