What does TPS do exactly - ie syptoms if bad

[RedRX]

Checking why the RX runs so rough, and thirsty- so going thru all the sensors etc. Throttle Position Sensor gets voltage, and shows resistance change from the idle position, but seems to send nothing back to the ECU - (as per the check connector). In other words - no variable voltage seems to be returning to the ECU. What would be the symptoms?

[Skip]

Red, the TPS is different on the hot wire MAF'd cars and the vane style, since you say you saw it change resistance then I'm assuming you have an 87 or newer hot wire car.

 

Symtoms, as you describe would run ruff, and may be in the limp home mode, very rich.

Do a plug cut to see or fit an A/F ratio gauge to see if it ever goes into closed loop.

 

You may have some wiring knackered if you see resistance change at the TPS and not at the ECU (of course the wiring to the check connector you used could also be bad.)

 

Have you checked the FI coolant sensor, it is a major player in the equation. It gets corroded from sitting in a vertical position and having it's boot get heat baked and cracked.

 

The TPS is one of the sensors the ECU watches and uses for shifting to the full rich map (when it thinks the engine is under a positive intake manifold condition i.e. boost) So if the signal is not making trip to the ECU you could be asking for trouble in the form of detonation.

 

The TPS also houses the "idle switch" BTW

 

Hope this helps

[RedRX]

Thanks Skip - that is exactly the info I was after. It is a flap-type AFM BTW. By the smell of fuel (and poor milage!) I think I am running full-rich. I have checked the temp-sensor - and it changes resistance as temp increases - which is what it should do I gather. BTW - any idea what a code 12 error is?

[Skip]

Red, email me - I'll look up the TPS test for a flap type in my FSM

Code 12 is the starter switch??

Here is a code chart

http://www.troublecodes.net/Subaru/

Hope this helps?