JimBobMaine

For what its worth, I'll just conclude by saying I put the old TPS back in, thoroughly cleaned the throttle body manually, and cleaned the idle air valve sensor. Its running normally, no CEL, no codes. My son says it occasionally stumbles when starting, but that's all. I returned the new TPS, and just wait to see what happens next. Thanks to everyone for your help!

So, I tried backprobing the connector, but not sure I ever got it right. I could get a signal, but it would never adjust greater than .41 on the return lead. I tried an ECM resetting technique of connecting the negative battery lead to the positive terminal for 30 minutes. No improvement. Put the old TPS back in, and it fired right up, idled and shifted perfectly. So that rules out vacuum leaks, or other systemic issues. The only two remaining explanations seem to be (1) need a reliable way to relearn the ECM, or (2) the replacement TPS is defective. Is there any way to bench test the TPS at home? I only have a generic multimeter to work with...

Sorry, its an automatic...is there an equivalent to the neutral switch on an AT?

Thanks! My next step was going to be vacuum checks, but haven't played with that much over the years...someone suggested spraying starter fluid around them, and listening for the engine surge. Not so sure about that one! The original sensor mounting screws were pretty much dead center in the slot...seems crazy that a half millimeter either way could send it so far out of whack. I really do appreciate all the input...spent all day yesterday messing with this, and I'm fresh out of ideas! Overall, I enjoy working on these old Subarus, but stuff like this takes the joy right out of it...

Since its an older vehicle, and it was the factory sensor, maybe it needs larger adjustments?

Agreed...I started out at the pre-existing adjustment, tried a few tweaks, but its still way over-revving. Also had no effect on the idle speed (1250 or so, vs 700 spec). I'm getting 5.12 V from the ECM, so that's not the issue. I put the old PCV back in, carefully cleaned the idle air control valve, rechecked all the connections, made sure I didn't knock something loose taking off the air box. I have half a mind to put the old TPS back in...at least it was driveable...not always start-able, but hey, its my kid's car. I'm happy to hear any other thoughts...

2003 Forester XS, 125,000 miles...for the last few weeks, it was wandering around its idle speed, difficult to start, finally threw the TPS code, so I swapped it out, and while I was there, changed the PCV, since I have no idea when it was last changed. Upon starting it up afterwards, I couldn't get the idle under 1200 rpm...adjusted TPS, adjusted bolts on throttle cable, no help. On test driving it, it would wind itself up to well over 3000 rpm before shifting, and it shifted very hard...on shifting 2-3, it took it almost to 4000 rpm, and again a hard shift. Now its displaying P0122, which is also a TPS code, and the TCM is flashing me 31 and 45 codes, for the TPS and the intake manifold pressure. I swear, I didn't touch anything...what the hell happened?