Put a rebuilt head on my 94 pickup. Engine idles rough and hesitates bad on acceleration. Timing is right and compression is good. When I unplug the Throttle Position Sensor it runs better. Do I need a new one, or could more be wrong in the EFI system.

Test the TPS and find out if it is good or not:

http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

I checked the TPS and it seems to be alright. I didn't have a feeler gauge thick enough for one of measurements, but all the others were dead on.

As noted on the web page, the exact feeler thickness is not terribly important. I have to stack up two leaves on my feeler gauge. But the idea of that test is the with the throttle fully closed, you get one reading and with it open a bit, you get another reading. Whether that happens at 0.5mm or 1.0mm or someplace in between probably makes little difference. The fact that it happens is what is important.

So it sounds like the TPS itself is fine, you might check that the signlas from it are getting back to the ECU properly. But it may be something else that is causing the problem. I think when you disconnect the TPS, the ECU goes into open loop mode and maybe some of the other bad inputs are ignored along with the missing TPS.

http://www.4crawler.com/4x4/CheapTricks/AFM/index.shtml

i recently had the same symptoms as you. i put a new engine in and a couple of days later it felt as if i put a race cam in the engine. it ran really rough. when you pull the TPS u sen the ecu into a limp home mode and all defaults are ran. I ended up testing everything like pickup coil,coil,tps and they were all good. when i pulled plug wires it ran better HMM running on 2 cyclinders i said. ok then try running a vaccum test to see how "Strong" your engine is running with a new head u should be at middle to high 20's. I did the test an i was only about 15. low vaccuum could be to tight intake valves. i think this is your problem because your head in rebuilt or new. new valves tend to tighten up during the break in. do yourself a favor and check the valves and let us know!! <img src="/forums/images/graemlins/cheers.gif" alt="" />

Redid the valves, nothing happening. I want to put another TPS on, but can't find one. Anybody have a spare TPS from a 94 pickup part #89452-12040?

Sounds like the symptoms of a bad o2 sensor

Got a new TPS from napa. Installed it, slight improvement, but still poor throttle response and hesitation. Have adusted and noticed big difference with TPS adjustment. Anyone have experience on tuning one of these in? Truck runs decent, but I have to floor it all the way. Circuit opening relay and Start Injector Time Switch exceeding recquired resistance. Any one have any experience with this? What happens when your ECU is fried?

When I bought the truck it didn't even have an oxygen sensor and ran fine. I have a bosch sensor now. Head is high performance...do I need to give it more fuel? Could my fuel injectors be clogged up or do I need better ones?

if the ecu was fried you "useally" get about 20 troublecodes. have u checked your EGR... do u have any codes the check engine light doesnt have to be on to store a code