89 jetta erratic idle

Hey there, I have an erratic idle when the car is at any temperature, Sometimes the rpms will rev up to 1200-1400 and hang there for a few seconds, and when it doesnt do that it will bounce from under 600 all the way up to 1400 sometimes going up to 2000. I have had the temp sensor(blue thing) replaced and it seems to have made the problem a little worse. I have no idea what it could be and the mechanic i am taking my car to isnt being very helpful. Would love any suggestions. My battery also died recently when i left my lights on when i went into work, could this have been a part of this. Thanks

Not sure which engine your Jetta has but I used to have a Jetta 16v which I loved and still miss to this day.
Here's some suggestions:
Change your mechanic - it sounds like he doesn't know how to fix it.
Is your throttle cable moving smoothly? sounds like something's sticking. If you have a carb something could be sticking in there?
Not sure about your battery prob really having much of an effect on the idle problem, but I might be wrong.
Hope I've helped.

Possibly a knackered Idle Control Valve. Is it an injection model?

Just realised another very old thread.