OK I seem to be having this issue too. I have a 3 wire vTPS off a 1.6 automatic, Wiring is correct.
Calibrating in TS is no problem. Ignition on, engine off, TPS sweeps from 0-100% without any issue, as seen here.
Engine on, signal is a bit jumpy and goes from a low of -30 to about 50-60% max. Checked calibration of zero throttle in TS, no change in value.
I measured the voltages at the wires with the engine off and on.
5v reference: engine off zero throttle: 4.96 engine off full throttle 4.97
engine on zero throttle: 4.96 engine on full throttle 5.00
TPS signal: engine off zero throttle: 0.65 engine off full throttle 1.99
engine on zero throttle: 0.65 engine on full throttle 1.20
Why do I have a drop in voltage at the TPS signal wire when the car is on?
Can anyone guide me on the steps I need to do? I did try running a new wire for the TPS signal and ran it straight to the 2L pin. Same thing.
Is it a ground issue? If so, how do I track it down?