Sorry about the dumb question, but here goes. When checking and adjusting the TPS voltage from the ECU, does the car have to be running at idle, or just the key be ON.?

 

Just - key on.

 

Not to argue....but I think either way is just fine IF the car is fully HOT. The FSM states that the car at IDLE should see APPROX 1VOLT at pin 2G (series four only). It's the green/red wire at pin 2G.

I've done it both ways. I just make sure the car is fully HOT prior to setting the tps. I know you know, but if you have a stock thermowax/fast idle setup on your throttle body, if the engine is cold, the thermowax/fast idle cam will cause the linkage to move. It'll cause the tps voltage to read high. Like around 1.6 or above volts. When the engine gets hot, the linkage returns to where it belongs and will read the proper APPROX 1V. reading.

 

The reason we can do this with just key on (after warm-up, as Mr Hailers highlighted), is that the ECU seems to output the same 5v ref to the sensors (seems to be about 4.9 for most of us) whether the alt is on (14v input to the ECU) or the key is on (12v input). Otherwise, we'd have to do it while running...