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97 Impreza OBS
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Discussion Starter #1 (Edited)
Starting a new thread for troubleshooting... I recently completed "ish" a 97 Impreza OBS to 02 WRX swap with the help of the wonderful people in this forum However, things still need a fixin :help:

-Copied from my old thread... -> I'm still ironing out a few quirks, (Main Issue) IAC code P0508 and Evap code P0457.

I've tried nearly everything short of getting a write up from on Demand on the trouble shoot process...

For my IAC code, the car idles fine. when I'm rolling and i clutch in,if I'm still in gear, my rpm will stay at 1200-1500 RPM. If I'm in gear and let off the gas the car will slow down until i hit about 1200 rpm then keep it's speed.

Things I've tried:
-Clean out IAC and throttle body
-Check continuity and OHMs at ECU plug to IAC (Passed)
-Replaced IAC Valve
-Smoke tested and did not find any leaks
-Compression and leak down test (Passed)
-Logs show Neutral position switch is working as intended
-Replaced AT ECU with MT one for the heck of it (did not fix code)

I'm at a loss. Has anybody else encountered this weird problem? Google search results show nothing about this problem.
 

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1995 EZ30 Coupe
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470 Posts
So I'm guessing it was an automatic WRX and now it's hooked to a manual? If so, is it wired to think it's in a particular gear when the car is actually in gear? Also, do the rpms behave normally if you shift to neutral while rolling? Is the VSS connected to the ecu and working?
 

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97 Impreza OBS
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21 Posts
Discussion Starter #3 (Edited)
Yeah, both the donor car and the receiver were automatic. I stripped the wrx TCM out, converted the bulkhead harness to accept a WRX manual trans and engine but, I had to leave in the OBS TCM in for ABS functionality.

I don't think the 02 WRX had a way to tell what specific gear it was in other than neutral?

Yes, when in neutral the RPM comes down to normal idle rpm 600-700.

The vss is in fact connected and working.
 

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1995 EZ30 Coupe
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470 Posts
Did you unplug one of the TCU plugs?

Edit: ok I'm guessing you did.

What I meant by specific gear was if you have it wired to be in 'D' or something while in any gear. I believe '1' would be a better option, but it probly won't make the difference you're looking for.
 

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97 Impreza OBS
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Discussion Starter #5 (Edited)
Ahhh I get what you're trying to say. Thanks for the idea! however, the WRX ecu isn't receiving any TCM signals. It's wired as if it were manual from the start.

The 97 OBS TCU sends some sort of signal it generates from the vss and wheel speed sensors* to the abs unit.
[ABS<->TCM- x -ECU]

The ECU knows that it's in gear from the neutral position switch located on the trans.
 

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1995 EZ30 Coupe
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470 Posts
Well, I'm just about stumped. I messed with the 'manual identification' pin and was able to fix some similar issues like rev hanging and such. I think it's supposed to be grounded for the swap but I floated it and it was happy? Just a thought...
 

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97 Impreza OBS
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Discussion Starter #7
Hmmm. According to the wireing manual I used, the trans identification pin needs to be wired to the same ground that the neutral position sensor gets it's ground from? If I find the link when I get home I'll post it.
 

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1995 EZ30 Coupe
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Yea, that sounds right from when I just did my Impreza. Like I said I had to fuss with it to get a normal idle and no rev hanging, but I can't remember exactly what I had to do. Thought it was contrary to common sense. :blol:

You know, maybe it's got something to do with your ECU and TCU combination, I remember reading something about the turbo TCU's being a little different. Or maybe the combo of different regions electronics?
 
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