99 f150 4.2 code problem

:banghead: I have a 99 f150 4.2 AT that is giving me a hard time. I currently have codes P1120 and P1121. 1120 shows TPS secondary voltage is low and 1121 shows the MAF does not agree with the TPS position. The truck had this problem when I got it but after running down the wire harness and all listed sensors on the VREF (refrence voltage to each sensor in the circut) I couldn't find anything else wrong with it. But clearly something is wrong outside of the computer. The voltage going into the TPS drops steadily when held at WOT. This means the shift points are really early and it will not downshift. Mileage sucks and no performance.

The DPFE was bad when I got the truck so I replaced it and since I could not find anything else wrong I assumed it took out the PCM. I mean I checked everything in the factory manual/CD and didn't find anything. Even pulled the upper intake and checked the EGR and passages - clean as a whistle.

Other things on this circut that I am curiuos about:
O2 sensors -
trans temp sensor-
trans shift solenoid -
trans output speed sensor -
trans position switch -
fuel tank pressure sensor -
Any of these things look like they could cause a drain on the VREF circut from the wiring diagram.

Anybody had a problem like this? That trans temp sensor is looking like a good candidate.... as the problem gets better when its cold out.
Thanks, Rob
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Youre on the right track 3 things come to mind .
1 check to see if your tp harness is routed closely to your ignition wires
2 unplug all your vref sensors 1 by 1 and monitor your tp pid to see if your voltage at wot has improved.of course the ones you can reach ie. dpfe,hegos etc.
3 corrosion in tp harness some place.may have to overlay circuit.

I am assuming you are looking at wot with key on engine off

lilvinny, thanks for the ideas, can you tell me more about the TP harnes being close to the ign wires? I'm thinking while I had the upper intake off they were prety close as in probably touching at the back of the block- right rear (passenger side) of the engine compartment. I have some new silicone wires and Motorcraft plugs to install but haven't done it yet, was trying to fix this problem first.

Thanks, Rob

Rob I was a tech for ford for 15 years and with the harness touching I have seen a voltage spike cross into the tp and iac harness usually a simple wire tie helps however it can damage pcm circuits.

lilvinny, that sounds like a realistic problem. The first PCM died and I replaced it after the DPFE. I have driven it about 15 times since re-assembling it - upper intake, harness, new TPS, PCM and the like, but the problem recurred. However, there is hope for the PCM, as the last time I drove it, it did well for about 2 -3 minutes. Hope there is a strong diode in that VREF circut! If not, I may put one in the PCM harness. I will seperate the wires and go back to pulling (hot) VREF connecters. It will be difficult to recreate the failure and find the problem. But I sure dont want to pay that shop rate...
Thanks again, Rob :)