Oldsmobile/Buick Repair: 1986 cutlass ciera code 21 problems, 1986 cutlass ciera, throttle position sensor

Question
i have an 86 cutlass ciera 4cyl 2.5 engine. with about 170,000.00 miles. automatic. i have had my throttle position sensor replaced about 2years ago and also had the spring replaced. after all this in the last month, when my car has been parked for about 30 to 45 minutes and then i back out of my driveway, the code 21 comes onand my car stalls, it seems to only happen when the engine is still hot and when i go in reverse. it doesn't do this if i go forward and the car has only been sitting for 30 to 45 minutes. my mechanic states also that the tps is hitting my throttle body when it moves and that i may need a new tb. i hope this information helps and that you can help me. thanks scott

Answer
Hi Scott,
The code 21 is defanitely associated with the TPS, but is also tied to a couple other criteria, such as vacuum reading, RPM, and a couple others.
When you are in reverse, do you have the brakes applied?
I am thinking vacuum leak in the brake booster.

The reason it would only do it when the engine is hot, is because some of the sensor signals are not used when the engine is cold, and therefore wouldn't effect it.
Van