1999 Ford Escort, SOHC 2.0L Ford CVH engine. Ford F4EAT electronically controlled automatic transmission -- PCM controls the up and down shifting.
no DTCs
First issue was that the car would have a stuck high idle sometimes. other times the idle was rough and would go up and down slightly. It has weird 1st-2nd shifts -- sometimes shifts early into 2nd gear, when creeping through a parking lot, foot not on pedal, it can't seem to make up its mind whether it wants to be in 1st or 2nd gear.
I was able to reproduce the high idle problem with a scan tool attached (FORSCAN computer software). Took car out onto back roads, put into WOT, went down the road, removed foot from pedal, idle went very high -- 3000 RPM. Put into neutral and safely pulled over, checked readings on scan tool. PCM reports part throttle, but the throttle plate was completely closed.
Duty cycle at 60% for IACV, which I think is fully open on a Ford. I opened the hood and pulled the lead from IACV. The idle dropped from just under 3000 RPM to 450 RPM. Plugged back in, idle shot back up to 3000. Turned car off and back on. PCM reports throttle closed, idles at ~800RPM, which is the correct idle for this car.
The closed voltage value for the TPS varied between several diagnostic attempts. Based on that, I concluded that the TPS was bad, and replaced it. I don't have a scope, but I think I need one.
Since replacing the TPS and resetting the computer memory, I haven't had any instances of it shooting up to 3000 RPM, but it still jumps up sometimes when you put it in park, maybe to 1200 or 1300 RPM, then slowly comes back down. The idle seems smoother. But it still shifts early into second gear sometimes.
I've checked voltages on the TPS wiring harness, and I'm getting 5V between the 5V line and battery ground, .01V between the TPS ground wire and the battery ground, and 3.57V between 5V and TPS signal wire (not sure if that one means anything).
One thing weird that I noticed is that there is a value called TP_RATE on the scan software. I don't know for sure what that means, but it often switches between 0 and something like 2048 . Anyone know what this does?
Any suggestions on what I should check next?
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