I've got a '91 Z28 L98, and have a few questions:

1) Why is my TPS on this car not adjustable? Could it be a aftermarket TPS, or do speed density cars not need the adjustment? Should I replace it with a adjustable one?

2)If I advance the TPS voltage will this have any effect on performance?

3) My car idle's erractly between 625-725 rpm. Is this due to a dirty IAC? Or is this just the lope on the factory cam? I don't think it's the cam cause the car stalls every now and then. BTW the idle screw has never been tampered with.... it's still sealed off with the cap.

4) Is there a link that show's in detail how to remove and clean the IAC? Can it be cleaned? Or should I replace it?

 

Try the search button.....


1. It should be adjustable.......

2. It will make the ECM go into Open loop earlier.....

3. The IAC could be caursing it

4. Search........

 

1. AFAIK SD car's come with a Non-adjustable TPS stock.

Nothing a little time with a file or dremel Can't fix.

2. No, it will not have a postive effect on performance. Adjust it to the stock setting and leave it be.

3.) The IAC could be at fault, as well as a million other things. There is no describable "lope" to the factory Cam, So that is not your problem.

4.) Check the Tech articles. It most definately Can be cleaned, and is most likely Very Dirty.

 

Trying to figure out a problem on an efi car witout looking at data from a scanner is just about impossible. With a scanner hooked up you could easily see two things. What the tps volts are and what the iac steps are. The tps is not adjustable because it doesn't need to be. The ecm reads it as a percentage. If it were out of whack you would get a TPS code. The IAC could be dirty, or stuck but the throttle blades could also be very dirty and not allowing enough bleed air so the IAC may be at it's limits in trying to control the idle speed. A TB cleaning should take care of both problems. Now, I have noticed a surging idle when a car jumps into closed loop and the o2 sensor is reading incorrectly forcing the car either way lean or way rich. A scanner will show this too, through BLM and o2 volts. When the car jumps out of closed loop it runs better and the cycle repeats itself, and it runs bad again.

 

I think Hector's right about the TPS non-adjustability. My 94 LT-1 uses one that looks VERY similar to your 92 TPI. It's non-adjustable except for a tiny bit of wiggle in the screw holes. The ECM doesn't look at raw voltage, it looks at the voltage RANGE as near as I can tell and then INTERPRETS throttle opening percentage from 0-100% (That's what Diacom shows on my 94). So it's kinda self-adjusting. I'm sure if it's way outta whack it would screw things up, though.

 

I enlarged the mounting holes on mine so it would adjust. After that it reads .50 to 4.8. No problems since.

RP.