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Old 06-17-2017, 08:27 AM   #1
Dvpper_sf5
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Default Erroneous idle

So I recently swapped one of those hardy 2.2s into my 1998 forester, the 2.5 DOHC had to go. Anyways after the swap I wanna say about 160 miles or so the car started to run funny at idle, and sometimes while just cruising, around 2k-2.5k Rpms it will bog down and act like it doesn't want to go anywhere. If I take my foot off the gas for a second and press it again it will run fine. Till it does it again. Some times at stoplights it will rev up and down and have erroneous rpms, anywhere from 250-1800 rpms. I know it goes this low because I've watched it with my scan tool. Also I'm throwing a DTC for the MAP sensor it's code P0106 range/circuit performance low.

Anyways I'm at a loss here because the car didn't throw this code before the swap. I've been to the junk yard and pulled close to 20 MAP sensors and tried them all. The code persists. I've tried to change the pressure sensor switch, pulled probably 10 of those from the junkyard. Code persists. I've checked, double checked and triple checked all the vacuum hoses on the diagram under hood. Even got lucky and found my EXACT motor at the junk yard, took pictures and ran the hoses that way, with that exact pressure sensor because it has 2 inlets and 1 outlet, as opposed to the one stock to my forester with 1 inlet and 1 outlet.

If it helps anyone my motor is from a 1996 Impreza L it's supposed to have a charcoal canister. But I don't have it. I have the vacuum lines for it ran in a loop, thy come out passenger side under the intake manifold. Could this be causing my problems?

Also a list of mods that may help I'm not sure:

3" full cold air intake, stock MAF box
1.75" custom single port EL headers, stock cats, 2.5" Tsudo catback

Any insight or advice or help is greatly appreciated it. I just want my car running properly again.
Thanks
HL
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Old 06-17-2017, 08:57 AM   #2
Charlie-III
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1998 Legacy 2.5GT
Silver Sleeper BK, 5MT

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I would lean to the IAC is dirty and hanging up. I think yours is on top of the throttle body, other spot would be sorta along side the throttle body on the passengers side.

As for the CEL, if you search it online it can also be the wiring, not just the sensor. Could be the device connection, wiring on the engine or further up the harness.
MAP engines are a bit easier in that they are not as picky with intake issues, I think your "loop" is fine, if it was an issue you would have had it from the beginning.

Clean the IAC, lots of threads on how to clean the various types here.
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Old 06-17-2017, 11:59 AM   #3
Dvpper_sf5
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It's an actual valve and not the sensor on top. I have 3 of those I've cleaned one and tried it. Code persists. I'm at a loss cause this DTC wasn't present before the swap. Could this be a vacuum issue? I've searched and searched online and in many other forums. I know this forum is very heavily used so I decided to join it in hopes of help.
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Old 06-17-2017, 12:01 PM   #4
Dvpper_sf5
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Also I've pulled the plastic wiring surround on the wiring pretty far back. I'm not new to the motor swaps or head gasket jobs on these cars. And I've been a service tech for the past 2 years so I'm certain no part of my harness was hurt in the swap.
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Old 06-17-2017, 02:02 PM   #5
Charlie-III
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Silver Sleeper BK, 5MT

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Quote:
Originally Posted by Dvpper_sf5 View Post
It's an actual valve and not the sensor on top. I have 3 of those I've cleaned one and tried it. Code persists. I'm at a loss cause this DTC wasn't present before the swap. Could this be a vacuum issue? I've searched and searched online and in many other forums. I know this forum is very heavily used so I decided to join it in hopes of help.
Depending on year and engine, the IAC is on top of the TB or down below on the passengers side of the TB.
The second one needs to have the cap marked before opening it up to maintain the setting.
Either version should have the air control vane move with minimal force when unplugged from the car.
Also check the IAC passages to make sure they're not plugged up.
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Old 06-17-2017, 02:29 PM   #6
Dvpper_sf5
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Yeah I've pulled one apart and cleaned it all and clean the passages on the manifold and throttle body and replaced all the hoses on it. Code and idle persist.
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Old 06-18-2017, 10:03 AM   #7
Charlie-III
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Silver Sleeper BK, 5MT

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You went from a 2.5 to a 2.2, what did you do about the ECU? The Forester should have been MAF and now you have a MAP?

What are your LTFT's like?

Have you tried resetting the ECU to see how it runs? Maybe it's learning something odd causing the issue.
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Old 06-18-2017, 11:37 AM   #8
Dvpper_sf5
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From what I understand this motor is supposed to be plug and play with that ecu. My forester had a MAP sensor and a MAF sensor. The MAP was on the passenger strut tower and the MAF was on its intake tube. They are both still the same. So idk what's going on
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Old 06-18-2017, 11:38 AM   #9
Dvpper_sf5
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Also I'm going back up to my shop to work on it in a little bit, I'll scan it while at idle and get some ltft numbers for you.
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Old 06-18-2017, 02:42 PM   #10
Charlie-III
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1998 Legacy 2.5GT
Silver Sleeper BK, 5MT

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A MAP sensor is usually in the intake tract (our 1999 2.2 NA was in the front of the air filter box), not on the strut tower. It supposed to measure manifold pressure, so it's in the intake somewhere.
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Old 06-18-2017, 10:11 PM   #11
Dvpper_sf5
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Default Erroneous idle

Quote:
Originally Posted by Charlie-III View Post
A MAP sensor is usually in the intake tract (our 1999 2.2 NA was in the front of the air filter box), not on the strut tower. It supposed to measure manifold pressure, so it's in the intake somewhere.

I get what your saying. But unfortunately it's not in my car. 1998 forester S model. They had the map sensor on the passenger side strut tower. My original 2.5DOHC was MAF. My ecu is set for MAF. I'm using a MAF.
My car also had/has a manifold absolute pressure sensor on the passenger strut tower.

My motor came from a 1996 Impreza L, it's a phase 2 2.2 liter I've seen this exact same motor, the older 2.2 with the charcoal canister up front in other imprezas and legacys and they too had a MAF on the intake tract, and map on the passenger side strut tower.

So what I'm trying to figure out is:
Is there any other reason the ecu would read this code? Besides the standard "it's a bad sensor?"
Why would it throw this after the swap?
It did not have this DTC prior to the swap.
Could a vacuum leak in another part of the intake tract cause this code to pop up?
If so, what are common places to check?
Could this code be coming from an IAT sensor that should be hooked up, but isn't because my 1998 Dohc did not have an IAT and the 1996 Sohc requires one?
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Old 06-19-2017, 09:02 PM   #12
Dvpper_sf5
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Also not sure if this helps anyone, but today while I was driving it, when I throttle to 1/4-1/3 throttle the car acts like it's bogging down and doesn't want to go anywhere, and it starts backfiring in a very weird fashion. Not sure if this helps with the problem
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