Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Some customers may comment on an engine vibration or noise while the vehicle is in gear at idle. This vibration can be felt in the steering wheel or seat and may intensify if the A/C is turned on. It should be noted that if the engine speed is raised or lowered approximately 50 RPMs, the vibration/noise will be reduced or go away.
A new service calibration has been released to lower the engine idle speed to 538 RPM in park/neutral and 525 RPM in gear. Before installing the new calibration, use the Tech 2® and go into Powertrain/Special Functions/TAC System/Engine Speed Control and when the condition is duplicated (engine running, in gear, foot on the brake, A/C on), command the idle down to 525 RPM. If the condition greatly improves or goes away, reprogram the PCM with the updated software calibration. This new calibration was released with TIS satellite data update version 1.75 available January 26, 2005. As always, make sure your Tech 2® is updated with the latest software version.
Also, if the vehicle is a 2004 model, Corporate Bulletin Number 04-06-01-023 may need to be performed.
#04-06-04-040: Idle Instability, Low or Rough Idle with Electronic Throttle Control (Clean Throttle Body) - (Jun 14, 2004)
Some owners may comment on an idle instability, low idle speed or rough idle.
Condition may be caused by deposits in the throttle body bore.
Clean throttle body bore and throttle valve plate of carbon using a shop rag and an appropriate cleaner. Refer to Engine Controls Repair Procedures - Throttle Body Cleaning Procedure. This procedure may be performed at any mileage necessary. Check to determine if the PCM calibration has been previously updated to one that includes the update for throttle body coking. For 2003 model year vehicles, look in the operating system portion of the calibration. For 2000-2002 model year vehicles, look in the engine portion of the calibration. If not, then update the PCM calibration to the latest calibration.