Throttle Position Sensor-Range Rover
You're on the right track as I've cured this problem several times by simply
cleaning the black gook off the steppers plunger as well as the seat in the
plenum that it mates with. Brake cleaner seems to work. Then once when that
wouldn't do the trick, it did turn out to be a throttle pot gone bad. You can
check it by connecting an analog ohm meter across the business pins and moving
the pot through its sweep. The needle shouldn't glitch at any point. Try
cleaning the plunger first, as it probably needs it anyway.
I found this website to repair the potentiometer:
What do you guys think? Anybody ever try this?