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Dan
Dan, Auto Technician
Category: Chevy
Satisfied Customers: 3490
Experience:  GM Mark of Excellence/ Service Guild Participant with 13 years experience, ASE Master Certified
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I have a 2003 Chevy Tahoe with the 5.3 liter. It has approx

Customer Question

I have a 2003 Chevy Tahoe with the 5.3 liter. It has approx 85,000 miles on it. It has been behaving fine until yesterday. It now has a problem with the idle dropping very low when sitting at a stop with the brakes on and the vehicle in drive. The idle will drop below 500 rpm on the tach, the lights will dim (due to the reduced rpm I would guess) and I can hear a "ticking" type of sound from the engine. The vehicle feels like it even starts to shudder from not being able to handle the load of just sitting there with the brakes holding it. When you do let off the brakes in order to start moving, it takes a moment to recover and the rpms come up once you accelerate. There are no fault codes being set. What should I look at in order to figure out what's going on with my wife's Tahoe?
Submitted: 5 years ago.
Category: Chevy
Expert:  Dan replied 5 years ago.
#05-06-01-006: Engine Vibration/Noise at Idle, Vibration Felt in Steering Wheel/Seat (Reprogram PCM) - (Feb 9, 2005)

Subject:Engine Vibration/Noise at Idle, Vibration Felt in Steering Wheel/Seat (Reprogram PCM)

Models:2003-2005 Cadillac Escalade
2003-2005 Chevrolet Tahoe
2003-2005 GMC Yukon
with 4.8L or 5.3L Engine (VINS V, T, Z -- RPOs LR4, LM7, L59)

 



Condition

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.

Correction

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)

Subject:Idle Instability, Low or Rough Idle with Electronic Throttle Control (Clean Throttle Body)

Models:2002-2003 Cadillac Escalade, Escalade EXT
2000-2003 Chevrolet Silverado, Suburban, Tahoe
2002-2003 Chevrolet Avalanche
2000-2003 GMC Sierra, Yukon, Yukon XL
2003 Hummer H2
with 4.8L, 5.3L or 6.0L V8 Engine (VINs V, T, Z, N, U - RPOs LR4, LM7, L59, LQ9, LQ4)
and Electronic Throttle Control

 

 


Condition

Some owners may comment on an idle instability, low idle speed or rough idle.

Cause

Condition may be caused by deposits in the throttle body bore.

Correction

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.

Dan, Auto Technician
Category: Chevy
Satisfied Customers: 3490
Experience: GM Mark of Excellence/ Service Guild Participant with 13 years experience, ASE Master Certified
Dan and 11 other Chevy Specialists are ready to help you
Customer: replied 5 years ago.
So I can try to "clean the throttle body bore and throttle valve plate of carbon using a shop rag and an appropriate cleaner" before I go to a dealership to see if "PCM calibration has been previuosly updated". What would be an "appropiate cleaner" for the throttle body bore and throttle valve plate? Are you refering to good old carb cleaner stuff? After doing so would it help to run some type of "fuel system cleaner" in the vehicle also? Is there any particular products that you prefer for this procedure? Thanks so far...
Customer: replied 5 years ago.
I removed the throttle body and I cleaned those parts all up with some carb and throttle body cleaner, I even usd a "scuffy" pad on the throttle blade itself until everything actually shined. There was alot of carbon buildup, especially where the blade would seal against the housing in the closed/idle position. It seems to have completely fixed the rough idling issue! My wife even said its so smooth now that its hard to tell if it's still running! Thanks for the advice on how to help with this problem!
Expert:  Dan replied 5 years ago.
You are very welcome and thanks for using JA.

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