I recently swapped in a mild 350 with a custom PROM(MAF setup). The car holds an idle pretty well and also runs pretty well although the readings on the IAC and TPS are pretty funky. The IAC counts stay at 160, when cold they moved around but after driving only a couple minutes, stayed put at 160 through the entire RPM range. The TPS reads nice at .58 with the key on and no pedal, but at WOT reads 1.25. I swapped in my spare TPS and the same readings.

Could it be related somehow, the IAC and TPS readings? Could it be as simple as re-setting the idle per the instructions? I will give that a try next but after that, not sure what it could be, or if that both readings are even related.

 

Sounds like the TPS is not wired correctly. Verify the harness matches the year of the TPS. The 95 wiring was diffeent pinout that my 87 and had me wondering till I checked it. Reset the IAC after the TPS is confirmed. then go back and reconfirm the TPS again after mechanically adjusting the TB opening for about 50 counts at idle.

 

There are three wires on the TPS. One is ground, one is +5VDC and the middle is the wiper. Verify that one of the wires has a constant +5V. If it doesn't, than either the wiring to the ECM is incorrect (OR OPEN) or you have a bad ECM. I have never seen an ECM failure like that but heh...it's possible.

 

I will try and test the wiring voltage next....

Would there be any way the high IAC counts lead to the low WOT TPS voltage, or vice versa? Thats my main question at the moment. I wouldn't think so but who knows...a coincidence both are reading whacky at the same time.

 

AFAIK, the IAC counts are strictly an output. The ECM monitors and controls the pulses and presumed postion as a result (counts), but that doesn't have any effect on the TPS, which is strictly an input.

The ECM provides a 5.0VDC reference to the TPS, and expects a signal between 0- ad 5V back from the TPS, but has no control over it.

I think the suggestions to check the TPS wiring and sensor are good, and may reveal a problem.

On the IAC, someone may have added a few counts here and there with a higher target idle to compensate for a different cam and/or modified intake.

 

I have...had the same thing on a '7730...it was a bad ECM.

 

Thanks for the replies again.

Is the ScanTool accurate enough for reading the TPS, or would a voltometer be even more accurate? I should have a chance to check it out this weekend and go from there, I have planned to get a spare ECM for awhile anyways as a good backup just in case something happens, so I might look for another one even if this one is fine.

 

Both would be accurate

 

The only potential problem with using the scanner to read the TPS is that the display will be what the ECM reads as the TPS voltage, but that may not be the ACTUAL TPS voltage. If there is a connection problem between the TPS and ECM, or if the ECM input signal conditioning or D/A converter have problems, the scanner data will be erroneous. The voltmeter will indicate the true TPS voltage, which may or may not agree with what the ECM interprets as the TPS signal (connections, input conditioning again). If the two don;t agree, there is definitely a problem somewhere.