I have a 1992 f150 5.0. Idles high after start up. I checked the tps wires and got 5 volts on the green wire and 11.8ish on the orange wire. The black wire, which I believe is the signal return, only has .02 volts and stays at that regardless of throttle position. I tested the wire harness from the tps plug to the main plug on the inner fender and got .4 ohms so the harness isn’t cut anywhere. I’ve heard the computer going bad causing this. Any ideas and help is greatly appreciated.

 

That orange wire should be your VREF (reference voltage that the computer feeds to a few of the sensors) it should have 5 volts max
See if that same wire has the 11 volts at the EVP sensor (VREF should be only 5v everywhere)
That VREF is supplied by the processor, which gets its power through the EEC power relay
I am looking at a 88 thunderbird EVTM for this info, but it should be correct enough
Your green wire is the signal return which should vary the voltage as you hit the gas .8-1.3v low and 4.5-5.0v high
You get that VREF voltage down and your problem will be solved IMO
The injectors get a 12v supply voltage, maybe you have a short somewhere?

 

Idles high after startup
Check it for an intake gasket leak and or plenum gasket leak

 

It should idle high after start up, then warm up, and slowly idle its self down. how high is idle after warmed up and driven, some?

This will help -->Throttle Position Sensor Testing, Replacement and Adjustment | Full Size Ford Bronco Forum

 

right at startup it shoots to about 1500-2000. Normally a good blip to the throttle makes it drop to 1000 and then after setting for about 30 seconds it’ll drop to 750 and it’ll stay there until I shut it off. Then processes starts over. Sometimes it’ll start and stay at 1000 rpm at start up but it’s very rare.

 

Mine does same thing, they all do, its how they warm up, with the ECM controlling it, like the old carbs with electric chokes, once you blip throttle, idle comes down, winter takes longer, I dont think you have anything to worry about, unless it starts hanging around, you can test/reset your IAC(valve)-->How to Clean and Test your IAC - Ford Bronco Forum

 

You need to figure out why the TPS voltages are out range. VREF should be 5.00 VDC +/- 10%.

 

I did the volt tests again and I told you backwards the first time. My orange wire is at 5.04, green wire is at 11.84,and my black wire is still at .02. I tried with two different tps sensors and got those exact results.

 

There is no way for the TPS output signal to be greater than VREF. VREF is the Orange wire, 5.04 VDC is textbook. TPS Output is the Green wire. It can never exceed VREF. Typical output is 0.6 to 5.0 VDC. Signal Return, Black wire, is a dedicated ground back to the computer for several key sensors.

What are you using as the ground reference, the black lead on your meter?

 

battery negative terminal. I’m following a guide from another forum. https://www.f150forum.com/f10/testing-tps-290537/ If his information is wrong let me know.

 

I just realized my mistake. I was testing ground not power.

 

That procedure is wrong for Tests 2 and 3. The Black wire is Signal Return. The Green wire is TPS Output/Signal.


Motorcraft TPS Wire Colors
VREF - Orange
TP SIG - Green
SIG RTN - Black

 

you were right. Redid the tests with your information and I have 12.30 volts to black wire (testing ground). 5.04 volts to orange wire (testing power) and .98 volts at closed throttle and 4.68 volts at wide open throttle to the green wire. With all that being said does everything seem correct.

 

Those results look much better and within specifications.