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2001 Forester STI 6 Speed Manual
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Discussion Starter #1
Hey I have a 1999 Subaru Forester S with the 2.5 SOHC Engine and 5 Speed Manual Transmission it's has 162,200 miles on it and recently the check engine light came on. On 10/29 my check engine light came on, I drove about 100 miles after that and didn't notice any problems, and when I went to my local Napa they said it was throwing a P0141 (O2 Sensor Heater Circuit Malfunction [Bank 1 Sensor 2]). So I planed on replacing the O2 sensor, but in the mean time it shouldn't cause too big of problems. Well ... 10/31 I was driving at around 35mph and the car starts jerking almost as if I were stalling out, I push in the clutch to bring it back down to idle, and it dies. I was unable to start my car after this until I waited for about 10 minutes, then it ran fine. This entire process repeated later on that day. Then monday I'm driving and in neutral it would rev up and down between 2,000 and 3,000 rpms. I read my codes again and now I have 5 ... P0141 Still and P1511, P1513, P1515, and P1517 which is all the high inputs for the Idle Air Control Solenoid. I have already removed and cleaned the Idle Air Control Solenoid and now if I rev it up to 4,000 rpm it stops and stalls?

What could be causing all these problems? Any help would be greatly appreciated, thanks Jonathon
 

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2005 Impreza RS Wagon Auto
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3,683 Posts
Try checking/cleaning your MAF to start, but if you are getting that many codes on that IAC then it probably needs to be replaced.
 

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2015 VW Golf R (AWD!) DSG (Automated Manual)
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If you decide to replace the MAF, let me know I have just the sensor itself I'll ship you (local parts places will only order the sensor AND housing which is 300+ bucks). I purchases a new one, tried it out, but it didn't fix my problem so back in the box it went :shrug:

As for your problem, it does sound more IAC related than O2 sensor. You might want to chat with some dealership technicians here and there and see if you can get a consensus...maybe drop in and inquire about how much it would cost to replace XYZ and if they think XYZ is really the problem?
 

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The 4000rpm limit i believe is the car in "safe mode" I would reset your computer, and clear the codes, the only time i have seen those one thousand eries codes they have been an error. And the couple times i have seen P0141 it has been the cats not the o2 sensor. Which kind of explains the problem you had.

when the car stalled and stuttered did it smell hot? if your cat is clogged it will through the p0141 code and cause the problem you are describing.
 

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What about the throttle positioning sensor. I assume that subies have them but i dont have experience on these. I had almost the same problem on my jeep and it was the tps. Pretty easy to check with a voltometer.
 

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2001 Forester STI 6 Speed Manual
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134 Posts
Discussion Starter #6
So, I've cleaned the MAF, IAC and replaced the rear O2 Sensor and it's running better, but still has sudden power loss or gain every once and a while, but it isn't stalling anymore at least that I've had happen. It now only has check engine light P1507. Any Ideas? Thanks a lot.
 

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P1507 says engine idle is higher than idle speed system is trying to hold. This usually means air is leaking somewhere causing high idle. System may hunt by closing IACV causing temporary drop, then go back up when IACV opens to increase idle. It means a large air leak which is overwhelming system ability to adjust. Check throttle body, intake manifold, brake vacuum booster line, and other vacuum lines for leaks.

good luck
 

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2001 Forester STI 6 Speed Manual
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Discussion Starter #10
After a while of driving the check engine light went off and has stayed off for the past 200 or so miles. The car starts and idles fine. The only problem I have now is the the loss in power Randomly while driving, and usually right after a shift I feel a loss in power like I removed my foot from the gas. The power will pick back up by itself sometimes or you have to give it a little gas, then it jerks and it's back to normal. What could be causing this problem? it's super annoying and inconvenient. Also it seams to me this is only happening when the engine is warm for the most part. Thanks
 

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1999 legacy
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I'm experiencing the same with my 99 legacy 2.2 brighton wagon automatic. 225000 miles on it. I've replaced the TPS with no luck, cleaned the IAC valve assembly and the Throttle assembly. the problem seemed to go away but is back again. while accelerating or cruising along it just cuts out as if someone took away the gas and then as I press the accelerator it cuts back on abruptly. IF in park i give it gas it wants to bog down and almost cut out and sputter. but left alone it idles okay. my code reader gives me consistently P1507. I'm thinking it's the IAC valve solenoid itself. I did the resistance measurement mentioned in the Chiltons and had infinited resistance readings across all three pins. voltage to it was fine. anyways that's where I'm at for now.
 

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You replaced the rear O2 sensor. This sensor only monitors catalytic converter performance. It does not affect drivability. I temporarily tricked this rear O2 function w/ the "$5 fix" on my 99 Forester to prevent P0420 code. It worked for over a year. I recently removed the fix when I found a loose exhaust joint ahead of converter and suspected this was cause of problem. So far code has not returned.

The codes you have for idle air control valve (IACV) are electrical codes indicating circuit faults and will not be cured by cleaning IACV. They suggest an intermittent solenoid winding in the IACV, loose or damaged connector, or faulty wiring. This problem, intermittent IACV, might be source of your performance issues. I would look for a new or used IACV.

Another suggestion to consider.
The forward O2 sensor can affect drivability and I have read posts similar to yours of surging, missing at steady speeds that was attributed to O2 sensor degradation. These problems occurred w/o primary O2 sensor code being set. I'm not saying this is your problem, but when you have an unusual problem w/o obvious causes, sometimes you have to "throw darts w/ blindfold on" and hope to hit the target. A universal O2 sensor can be purchased very inexpensively on ebay. It requires wiring to your harness, but simple instructions are provided. I've done this and found the universal O2 sensor works fine.

good luck
 

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2001 Forester STI 6 Speed Manual
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Discussion Starter #15
I unplugged the TPS today and all the problems have gone away for the past 60 or so miles. Though now I'm getting a check engine light from it being unplugged. Is there anyway to clean or adjust the TPS? to try and avoid replacing it. Thanks
 
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