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I am writing today in hopes of getting pointed in the right direction. Background, I have a 1995 Bronco XLT with a 5.8L and E4OD (I am sure the F-150s would be the same). Since buying it, I have a high idle when it is warm, in neutral, and A/C off. I have checked, double checked, and triple checked for vacuum leaks, set the TPS correctly, swapped some sensors from another vehicle, pulled codes, switched PCMs, etc. Even changed the plenum and intake gaskets. I can 100% verify it is not cause by a vacuum leak or a bad sensor issue.
I have discovered it has something to do with the transmission. I will have the truck warm and its idling at 900rpm to 1000rpm. I unplug the MLPS connecter from the sensor and the idle drops to a proper 650-700rpm. Plug the connector back in, it idles back up. Ok, so I changed the sensor convinced it was the issue. Even with a new sensor, it acts the exact same way.
So my question is, can someone explain how those circuits work, and how to check proper function? I want to verify the correct wires have the correct voltages during the correct shifting points so I can see which circuit is causing the high idle. I tested the MLP sensor signal and get 5 volts with the key on. What I need to know is does the sensor signal return see 5 volts at some point during shifting that tells the computer to idle up when shifted into gear? I assume it is designed to increase idle when in gear to compensate for the addition engine load.
