I had to slot my TPS in the past for my aftermarket throttle body. Everything worked good for over a year. Now I have high idle problems because my pcm thinks I'm holding the throttle open.
According to my scanner:

With the engine off, the voltage reads .69 volts and the throttle positions is 0%. I have to push the throttle open to about .8 volts to get any change in the throttle position reading. When I release the pedal, the voltage always goes back to .69 volts and 0%. This looks good.

With the engine on, the TPS reads about .69 volts and the throttle position reads 0. When I tap the gas, the tps voltage will go up and then come back down to .71 and the throttle position will read .8%. I tap the gas again and it will go to .72 volts and 1.2%. If I side step the gas pedal, it will go back to .69 volts and 0%.

Ok, why does .72 volts=open throttle when the engine is on but I have to go all the way to .8 volts with the engine off?!! What's going on? If I could maintain the .8 volt threshold with the engine on, I would not have a problem. I have not put a volt meter on the tps yet but I'll do that tonight. Has anyone had this kind of problem?

 

well, I adjusted the throttle stop to a different position in case it was just some hangup in the throttle body spring. I slotted the tps some more. So now I have .6 volts at 0%. The problem resurfaced this morning. I find that restarting the car when it is high idling fixes the problem since it resets the tps. It looks like the throttle body is just sticking. I tried to clean it last night. But on a positive note, I replaced my knock sensor last night and all of my knock retard is gone!

 

What 58mm throttle body are you using? Have you tried more tension in the return spring?

 

Its a BBK 58mm throttle body. By more tension do you mean a different spring? I tried resetting my throttle stop to give me a little more tension in the spring.

 

I have a Holley 58mm, and there are a couple different holes in the side of the TB body that the end of the spring can be inserted into. You can add or reduce tension by moving the end of the spring, which tightens or loosens the coiled spring. Not sure what the BBK looks like, or whether it has a similar adjustment. I did just see a pic someone posted of a straight spring he added running from a pin on the side of the throttle body quadrent to the cable bracket.

 

Thanks Fred, that would have been a great feature, but my spring just rests against a boss on the throttle body. There are two arms on the shaft. One vertical arm has the spring on bottom end and hits the stop screw on the top end. The second arm is the quadrant. It seems that there is some play between the first arm and the shaft. I don't know yet if it is enough to cause the problem (I have to check with the scan tool). I'm also wondering if, despite the vortech bypass valve, I'm getting enough intake hose pressure combined with enough manifold vacuum to drive the throttle open. I see this problem when throttling down quickly or when I goose the throttle. In any case, it doesn't seem to be a computer problem. I'll try that straight spring idea. Thanks!