Driving through town yesterday I had the check engine light come on and the transmission fail to respond to a forced downshift. That is, when I pushed the throttle it would only lug in the current gear.

I assumed I had a TPS issue and pulled the codes today. The code was TPS stuck high. So I replaced the TSP and no change.

I put the scanner back on it and monitored the TPS voltage via the scanner. TPS voltage never drops below 2.74 volts and will rise in a linear fashion to 4.79 volts as you press the throttle.

I put a meter on the TSP and it works normally with the signal going from less than 1 volt to 5 volts as you turn the sensor.

So what would cause the ECU to see 2.7 volts to 4.79 volts when the TPS is working normally?

 

I had a 95 E150 act up suddenly "way back when", the transmission started going haywire, not sure if it's anything like yours, but the speedometer ended up having to be changed. Apparently you can change tires sizes only about 5 times before the speedo has to be recalibrated, I was on about the same number of tire changes. Had something to do with the 4 wheel antilock brakes

 

Well, its clearly not the speedo. The tire size is OEM and the MPH on the scanner is correct.

This is clearly a TPS voltage issue. The Scanner data says the TPS voltage is too high even when the voltage at the TPS is correct.