AutoEngineer
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I work in engineering with car OEM's as a career. I became involved in this issue when I saw my sister in tears over the fact that twa GM Dealerships were unable to fix her car after trying for over a year. She still owed thousands on it and had spent much more on top of that trying to fix it. I took the vehicle for a week and was able to diagnose and repair the issue. It has been running flawlessly since. Due to the desperate nature of the problem -since it really is out of the dearships hands to repair, I've decided to share this in hopes that it will help anyone else with this same issue:
The TPS sensor is physically connected to the throttle (butterfly valve) via a spring-loaded connection. The TPS sensor’s "wiper" on these throttle bodies has a bad habit of wearing into its pivot points over time -to the point where they start gouging into adjacent metal surfaces instead of just riding on top of them like they did when they were new. This results in binding of the wiper to the point that the aforementioned spring-loaded connection gives before turning the wiper on the TPS sensor. When that happens, the TPS sensor doesn't track with the throttle and -bam: A-B throttle correlation codes (for obvious reasons), traction/stability control codes (due do the resulting unstable engine RPM), and reduced engine power (the ECM doesn't see the throttle responding as demanded, so it limits power). Watch out; almost all throttle bodies applied in service are remanufactured and can come with this same issue built in. Ironically, the dealer can't do anything since the TPS sensor is built into the throttle body, and they’re not allowed to tear it apart -but you can. This can be repaired at home. Here’s how. Disconnect the electrical connector and simply remove the 5 or so clips with a screwdriver to remove the throttle body cover. Don’t worry; the clips can be pressed back in place by hand. You'll see a metal plate in there, behind which the TPS wiper resides. You can break off the 5 heat stakes (plastic nubs melted over the plate to hold it) with a screwdriver and remove the plate. Remove the wiper and put some silicone-based grease in the areas where it pivots against and then reassemble it. In order to hold the plate back in place, you can drill two holes adjacent to the top surface of the plate -from the inside of the cover, out- one each side of the plate. Then, from the outside of the cover, screw in two small screws just far enough that the points hold the cover down. Reassemble the cover onto the throttle body.
The TPS sensor is physically connected to the throttle (butterfly valve) via a spring-loaded connection. The TPS sensor’s "wiper" on these throttle bodies has a bad habit of wearing into its pivot points over time -to the point where they start gouging into adjacent metal surfaces instead of just riding on top of them like they did when they were new. This results in binding of the wiper to the point that the aforementioned spring-loaded connection gives before turning the wiper on the TPS sensor. When that happens, the TPS sensor doesn't track with the throttle and -bam: A-B throttle correlation codes (for obvious reasons), traction/stability control codes (due do the resulting unstable engine RPM), and reduced engine power (the ECM doesn't see the throttle responding as demanded, so it limits power). Watch out; almost all throttle bodies applied in service are remanufactured and can come with this same issue built in. Ironically, the dealer can't do anything since the TPS sensor is built into the throttle body, and they’re not allowed to tear it apart -but you can. This can be repaired at home. Here’s how. Disconnect the electrical connector and simply remove the 5 or so clips with a screwdriver to remove the throttle body cover. Don’t worry; the clips can be pressed back in place by hand. You'll see a metal plate in there, behind which the TPS wiper resides. You can break off the 5 heat stakes (plastic nubs melted over the plate to hold it) with a screwdriver and remove the plate. Remove the wiper and put some silicone-based grease in the areas where it pivots against and then reassemble it. In order to hold the plate back in place, you can drill two holes adjacent to the top surface of the plate -from the inside of the cover, out- one each side of the plate. Then, from the outside of the cover, screw in two small screws just far enough that the points hold the cover down. Reassemble the cover onto the throttle body.
