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Old 03-30-2009, 04:52 AM   #1
Scooby Specialist
Member#: 27136
Join Date: Oct 2002
Default TPS Sensor replacement / specs on 94' Ej18 .. Cold / hot voltage?

I just replaced my TPS sensor on my 94' impreza, and I have nothing but a vague Chilton's repair manual to help me.

I am trying to find out if there is a cold engine / hot engine resting voltage spec for the TPS sensor? My chilton's is very vague and gives fully open / closed resistance measurements on the TPS but they don't even match.

I think my car has a coolant temperature sensitive cold-start warmup valve.. or whatever you call it. The valve acts as the throttle stop and when the engine is cold, keeps the throttle plate open slightly to elevate engine rpm until the coolant temp raises and then slowly closes it according to coolant temperature.

Right now, I have the TPS adjusted to 0.500v while the engine is cold, but I only realize that might be wrong.. 0.500v is usually when the throttle is ideally closed all the way, so I should wait until the car is at operating temperature so that the coolant temp valve is fully "open" or the throttle plate is fully closed and the warmup phase is complete?

I'm not sure if the OEM service manual has any mention of this. All I know is that the TPS has at least a 1/8" to 1/4" of adjustment.. easy to screw up.

I would think the coolant valve will open the throttle plate to about 0.580v or higher, then drop to about .5v?

Just need some guidance on this. My old TPS sensor would go OPEN during warmup so the engine would want to die at the first traffic light on a cold morning..

It runs fine now but I want to make sure I install it properly!
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Old 03-30-2009, 03:46 PM   #2
Scooby Specialist
Member#: 19239
Join Date: May 2002
Chapter/Region: NESIC
Location: QC
2011 WRX


There is no warm/cold voltage difference on the TPS. Factory manual has 0.2-1.0V closed and 4.2-4.5 open on the signal wire (blue/green).

The idle air control valve is what controls the idle when the throttle is closed. The ECU reads the coolant temp in the crossover pipe and decides what the IACV should do. The IACV is a waveform signal.
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