rryan1988

ok so ive been told by hundreds of people that my TPS is screwed, the idle goes up and down once the car is warmed up, i see all the forums on how to test the TPS, however i havent seen anyone strictly say how to test the TPS on a speed density engine, is the test the same for a MAF enigne and speed density?

N3mi5is

Yes. Check the voltage of the TPS at idle, and also check the resistance of the sensor throughout the full range of throttle opening to check for opens in the sensor.

To address the idle up and down issue, check for and eliminate any vacuum leaks. I just did this to my '87 speed density, and no matter how many times I reset the idle (would idle great when cold) but at operating temp it would idle up and down severely. I found a total of 6 different vacuum leaks (old lines, previous owner removing emissions equipment and not capping anything off etc). It idles like a brand new car now with all of the leaks repaired.

rryan1988

Ok that seems simple enough, how did you test the vacuum lines? just a propane tank and slowly move it around the lines? and the TPS is there a way to test it without backprobing the wires..?

HeliFreek

I had the same issue a middle of last year. I checked the TPS, it was ok. I could not find any vacuum leaks. So I decided to try some throttle body cleaner. First I disconnedcted the CA intake so I could see the throttle body and I sprayed into the TB. Then I started the car, it was rough starting but eventually it started. Then I sprayed more into the TB, I had to blip the throttle to keep it from dying. Once all that was done, I sut the car off, I let the car sit for a few minutes and then restart the car. The idle up and down is gone, now 7-8 months later and about 2000 miles.

Mark

87 T TOP GT302

I didn't read anywhere but is the car stock or have you modified it any ,heads cam,ect?Since i've installed the cam in my GT it won't idle anywhere but 800 rpm's.If I try to raise the idle it goes in the up down idle but at 800 stays put.I'm just glad it works.Also check your idle air control on the side of the throttlebody.If it gets gummed uo it can cause this too.Take apart and clean w/carburator cleaner and a tooth bruth.

HeliFreek

The 86 is stock except for a BBK CAI and flowmaster mufflers. The IAC is clean. cleaning the IAC didn't help in my case. A good friend of mine, who is also a mechanic and Ford is what he knows best, checked the TPS and said it needed a little adjustment. I watched him adjust it, it was the same way folks had described on this site. Knocking on wood....... the car still idles as it should after over 3000 miles of driving.