Question: My original problem with my 2004 Silverado 5.3-liter was a surge at idle when warmed up. I was told that cleaning the throttle body should fix it. There is no throttle cable. I took off the throttle body, but couldn't remove the sensor from the side. I cleaned it inside and out with carburetor/throttle body cleaner, and put it back together. But the surge problem is still there, and now it sometimes revs high. It will stay at about 1200 rpm when I come to a stop, but only once in a while.
Answer: You're dealing with electronic throttle control (there's no throttle cable anymore). And the sensor that wouldn't come off most likely was the throttle control actuator (motor), which moves the throttle plate open and closed. On every ECT throttle body assembly I can think of, the actuator is riveted to the throttle body housing, and therefore is not a serviceable part. There's way too much liability involved to have a technician or anyone else tampering with the mechanism. When there's a problem, you must replace the entire assembly.
Yes, there are issues with "coking" or carbon buildup on the throttle plate, which can cause a rough or unstable idle. This typically occurs on higher-mileage engines, and requires a careful cleaning of the throttle plate and bore with a shop rag and the appropriate solvent, preferably GM Top Engine Cleaner.
What concerns me is a different problem (high idle) taking place after you did the cleaning. Saturating any electronic components, or damaging the throttle plate or bore with a metallic object, will require replacement of the complete throttle body. Disconnect the positive and negative terminals on the battery, short the two terminals together, turn the ignition on, and let it sit for about 15 minutes. Then hook everything back up. This will completely clear the PCM memory. Let the engine warm up to operating temperature, and then idle for about 15 minutes. This should allow the PCM to relearn the correct position of the throttle plate. If this corrects the problem, you're good to go. If not, bring it to a Chevy service department and explain the situation. There they can perform a PCM software update designed to correct a rough idle condition on your particular model truck, and at the same time, inspect the throttle body assembly for damage, or any other faults affecting idle quality.
How To Reach Alex
If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at firstname.lastname@example.org. Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.
Can't wait for help with a problem you're having with your Truck or SUV? Ask the expert we trust here at Truck Trend Garage -- visit Alex Steele at www.RealWorldAutomotive.com.