I have a 1989 F-250, 351W with C6 trans. The vehicle was parked for two years with idle problems. I checked the codes and had EGR and TPS codes. Replaced the EVR, EVP and EGR valve along with hoses. Replaced the TPS, cleaned the IAC and replaced IAC and TB gaskets. Still have code 53. Checked the TPS resistance at TP SIG and SIG RTN with 5680 ohms at idle and 728 ohms WOT. Back probed the TPS connector and had 5.03 volts at idle and WOT. Vehicle starts with high idle that steps down and then stalls. If I hold the throttle briefly it will idle and run fine. CEL is on during this time. On occasion, at around twelve miles of constant driving the idle will "change" and the CEL will turn off. Any help would be greatly appreciated.

 

Sounds more like you measured the VREF signal instead of the TPS signal back to the PCM. I always use voltage values when measuring a TPS.

 

Since there is already a new thread on Throttle Position Sensors, I thought I'd add to it. When replacing the TPS are you supposed to put dielectic grease on it before installing?

 

I do put some on the connector to help keep moisture out.

 

The old one had some on the part the mounts on the throttle body.

 

Hey Cage Fighter, This may help you some.

YouTube - Testing a Ford 5.0L throttle position sensor

 

Texas Guy, thanks for the link. I'll give it a check tomorrow and see what I get. I had considered that there might be a problem with the connector and this should confirm or eliminate.

 

OK, ran the tests according to the video and all was fine until the SIG RTN. Should have had approx. 1.0V at idle and had approx.10mV with no change at WOT. It looks like I might have a short somewhere.

 

Minor correction, the Signal Output (Not Signal Return) in the video was ~1.0VDC at closed throttle throttle then progresses to ~4.5VDC at WOT. FWIW the closed throttle voltage can be anywhere between 0.6 - 1.0 VDC.

You said you measured the TPS output with an Ohm meter in your first post. Did you ever look at the resistance from the VREF wire and Signal Return and/or Signal Output? The TPS could be open internally.