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Old 01-31-2008, 10:13 PM   #1
creepyoldguy
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Member#: 67319
Join Date: Jul 2004
Default ECU throwing apparently bogus IAC codes

So hopefully one of you can diagnose something a whole bunch of mechanics and the subaru dealer have yet to figure out. Please bear with me, it's really complicated:

about 2 years ago my 02 impreza outback started bucking around at low speeds, and occasionally temporarily dropping fuel pressure at constant speeds in higher gears. The check engine light came on and multiple mechanics diagnosed an IAC problem.

I paid lots of money to have the little bugger replaced and the car drove happily for about a day, but then exhibited slightly different/lesser versions of the same problem.

These are the new symptoms as best as I can describe them:

slowly accelerating through 1st gear works fine until about 10-15 mph, at which point the car abruptly loses fuel pressure (or maybe air?) for about half a second, but then quickly kicks back in again. When gently easing off/on the accelerator while it's in gear (especially 1st gear), the car acts like i'm being really clumsy with the pedal and bucks around. if i throw it into 1st gear and let the idle drive it, it goes smoothly for a little while then develops a slight rhythmic bucking, then it gradually increases until it's like riding a spastic bull... bordering on engine stall. the problem is more pronounced on very hot days, when the fuel tank is nearer to empty, and when the AC is running. check engine light on the whole time.

i went back to the same mechanic. soon as i get 1/2 mile within arriving at their lot, the check engine light goes off and it drives smoothly, as if there had never been a problem. they can't make the car display any symptoms, but say the ECU had thrown the IAC trouble code. we replace it again under warranty. i drive it off their lot and 1 mile away, check engine light comes back on, car goes right back to driving funny.

i take it back the next day... 1/2 mile from the mechanic, engine light goes off, starts behaving fine. the mechanic scratches his head and says he can't find any problems to fix. 2 miles off their lot, engine light back on, car jerking around again. i take it to the subaru dealer. they reset the computer. 1/2 mile away from the subaru dealer, engine light back on, same old problems. i take it to an aftermarket subaru specialist. they dig through everything, find some very small leaks on some hoses. they seal them up, change spark plugs. car drives fine for a day, then same problem again. i take it to a different mechanic for a timing belt/water pump. he says it's still throwing idle air control problem codes! then out of nowhere, the AC compressor stopped kicking on. Now sometimes the AC works, sometimes it doesn't. I took it back to original mechanic who replaced the IAC. He tests the valve and finds it to be working properly, says that ECU is throwing erroneous codes. "Maybe it's a bad computer..." I call subaru, who tells me that a computer acting strangely probably wouldn't be the culprit of the symptoms I had described.

What the heck is going on here? This car is driving me insane! Any help is much appreciated.

Thanks!
S
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Old 02-01-2008, 04:33 AM   #2
mikndee
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Member#: 169433
Join Date: Jan 2008
Chapter/Region: South East
Location: jacksonville nc
Vehicle:
2010 wrx
rally blue

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just trade it in on a good day, i know thats a crappy answer but i had a 2001 civic that did crazy stuff on random days a while back and i just said f-it and bought a 04 rs. the funny thing is the honda only had about 55k miles on it when all sorts of wierd stuff like that started going on. i just chalked it up to a random bunk one i got. the funny part is that i got a premium trade in value for the civic and a great deal on the subaru but i went back to the dealer about 6 months after i got the new ride and they still had the civic. the manager was mad that he gave me so much for the civic and he couldnt get rid of it. i did spend like 4 hours haggling with em though.
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Old 02-01-2008, 11:01 AM   #3
creepyoldguy
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Unhappy so nobody in subaru land has seen these symptoms

correspond to anything in particular?
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Old 02-01-2008, 12:38 PM   #4
mikndee
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Chapter/Region: South East
Location: jacksonville nc
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2010 wrx
rally blue

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i try to forget the crap that i suffered with the car for the time it acting up. but, i remember that it would be driving fine and start bucking, loss of power, wierd idleing, check engine light coming on for no reason. similar stuff. it very well could be an ecu problem, distributor problems, timing etc. thats what the mechanic was sayin then. i remember having to have the pedal down an exact amount no more no less to get some smoothness. it was an auto so it was probably easier to get some conformity. i just drove it in real carefull and did everything i could for them not to move it before i drove off with a new car and a signed contract. i wish i could help more i not a mechanic or anything.
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