I have a 1989 Chevy C1500 (4.3 V6). It had a weird idle when it first started up. It occasionally stalled at red lights, in drive. I was told that the Throttle position Sensor needed to be replaced. I replaced it. Started the truck and it idled pretty good for a few minutes but then it loped real bad and almost died. The Service Engine Light came on. I disconnected the battery to clear the codes. Hooked it back up, started the truck and the light is still on. What is going on with this thing? Please help.
The first thing you should of done was to have a qualified mechanic put a scanner on the truck to see if there was a code stored in the computer memory.
There are many reasons that can cause an engine to run rough and surge.
The most common faults are a vacuum leak at the intake manifold or throttle body gasket, spark plug failure, spark plug wire, distributor cap has moisture in it or is cracked, throttle body injector clogged, map sensor or vacuum hose to the map sensor is leaking, Idle air control motor is faulty, the list can go on.
Changing the TPS should not cause a problem unless it is installed wrong or is over tightened making the switch jamb up inside. Make sure the injector wires are not crushed under the air cleaner. This is a common mistake.
Before you do anything else have someone scan the computer for codes. If you don't know anyone then Auto Zone will do it for no charge and tell you what the code is. Then you can continue with your diagnostics.
There is a chance it is something else and it is a different code than the TPS code.
Keep us up to date on your progress, we can diagnosis the problem further once we know what the code is that is turning on the light.