There is a service bulletin for that issue on your truck. The correction is to clean the throttle body and update the engine software. You can clean the TB yourself but a dealer may do this for you for free. Let me know how this works out. See bulletin below. Bulletin No.: 04-06-04-040 Date: June 14, 2004 TECHNICAL 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 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.

Thank you for the information. My 2003 very low idle, but not yet dying. Idles about 450 RPM. Again, Thanks.

How much should this cost at a Cadillac Service Department for a 2003 Excalade EXT?

You need to clean your throttle body. This is a common problem with the intake on Vortex engines. The dealer will charge about $150 to do it and you will have the problem again in a year or two. You can fix it yourself in about 10 minutes with no more than a flat screwdriver, a rag and some acetone or carb cleaner. Take off the clamp where the large intake hose feeds into the throttle body, carefully pull the hose off of the throttle body take a clean rag with either acetone on it or carb cleaner on it and clean the inside of the throat of the throttle body. As you look in the tube, you'll see a flap valve and you'll see oil buildup between the bottom of the flap and the tube. Just carefully push the bottom of the flap back and clean that area. Put the hose back on and tighten the clamp and you'll find the car will run like new again. Good Luck!

is it possible that my truck(2004 sierra) wont throw any codes?? cause i have the same problem just no codes at all.