I have a 1990 Sidekick that is constantly idling up and down. It runs from 1000 rpm to 2000 rpm constantly. I have been told that it is the throttle positioning sensor. Does that sound like what it is? They are $170.00 and I don't want to buy one if it is not the problem. If this is not it, what else could it be?

Junkman

I would say that its probably not the TPS if its an idle problem and the TPS is correctly adjusted. have you got a Check Engine Light on? Take a look at this site:

http://www.kick-fix.com

Thanks! I'll give it a try.

I had this problem with my 1990 Tracker.  One thing I found mentioned was vacuum leaks.  Mine would do it until it was warmed up.  I also had a high idle on startup.  Both these problems were fixed when I blocked off the air to the wax pellet that controls the high idle.
 It's to the passenger side of the tps.  A cover with 3 screws, remove the cover and there is a spring loaded valve  and the wax pellet is behind that.  I have a factory service manual that showed how it looks.  I used a piece of rubber hose ---with a small bolt part way through to keep it straight--- to fit over the opening to block off the air.  I needs to be about 1" long.
This fixed the idle problem.  No more surging and no 3000 rpm on start-up.  It won't have a fast idle when cold but I haven't had problems with that since these engines warm up pretty fast.

You can search for "wax pellet"  or check out this
 http://www.zukiworld.com/forum/general-suzuki-forum/wax-pellethigh-idle-fix/msg93396/#msg93396

Hope this helps.

Hey! Thanks alot! That was exactly what was wrong.

Junkman