Code 21, TPS voltage reading backwards

Hi Guys,

I have a '92 chevy 1/2 ton 2wd w/350 and auto.

For a couple years now I've been fighting an issue with a high idle and an occasional code 21, tps voltage high. I'm not new to these systems but am stumped at this point. The problem was intermittent and is now occurring more often so I'm forced to fix it. Most of the time the truck will just idle high and throw no code. It idles so high it will spin the rear tires on ice when stopped. I have installed two tps that I got from a local parts store. I suppose it's possible I got a bad batch but I don't know. I have a good 5v reference signal to the sensor but the sensor reads 5.0 v at idle and .8v at WOT. That's backwards. I am going to replace the sensor tomorrow because I did notice a dead spot in the sensor when moving it from idle to WOT but I can't figure out why the reading are opposite what they should be. The tps can basically only go on the tbi one way and I've replaced many of them on other trucks in the past with no issues.

Also, could I have a bad computer? I have checked the ECM ground, tps gray and dark blue wires to the ECM, MAP wires to the ECM and they are all good.

Any thoughts would be appreciated.

Thanks,
Jason

Back probe wire at sensors. With ground on block and pos. back probe dr blu on TPS, this is your TPS signal. Gray is 5 volt ref, and bl is ground. Map do the same, Lt gr is map signal, gray 5 volt ref, ppl is ground. The only other thing I can think of is , when you install tps make very sure of how you put it on. The blade that turn the tps has to be install correctly.

Well, I replaced tps and eliminated the dead spot. I also removed and cleaned all grounds and added new ground from intake to body and frame to body.

Truck seems to be running fine and tps adjusted to spec with no problems. We'll see what happens.

Man....those grounds will bite you in the rear everytime!