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Old 01-30-2012, 08:54 PM   #1
RolySaul
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Default Very Intermittent Symptoms coupled w/p0420

After reading many p0420 threads, and posting my questions, I got a LOT of good info here which I really need cuz I'm really not up to your guys' knowledge level.

I had cleared the p0420 code before reading some useful advice about why not to, and it's back, but now I'm a little more tuned in to what to watch for.

The car runs perfect for many miles, then for no apparent reason other than the weather is cold here, about freezing or slightly below most days, I get the following while the car is plenty warmed up....

The car will just bog a little, on a slow acceleration, I DO get a whiff of "rotten eggs" which I now understand is a really bad rich mixture, it will tend to idle really low when letting off the gas coming to a stop -and in fact stalled out a at a couple of red lights. Then sure enough, p0420... Then it runs perfect for a good long time as in a hundred or so miles with no problems at all.

So because it is so intermittent I am still in the dark.... I'm still reading threads and trying to get up to speed.

Is replacing the front a/f sensor going to be a reasonable thing to try ? I live in a condo and can't work on it here, and I'm reluctant to do anything outside in the cold by the side of the road. If it's going to cost me a hundred labor or so that's ok, I just don't have the means to do it myself sometimes PLUS I don't want to take on something where I could easily break something and make it worse.

I know there's a difference of opinion here on the p0420 code, but given the symptoms, are there simpler things I can look at with a novice eye and maybe find something obvious and tinkerable in the engine compartment before I take it to the shop??

Sorry for the long post guys, if you're still with me at this point thanks.
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Last edited by RolySaul; 01-30-2012 at 09:09 PM. Reason: edit for clarity/spelling
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Old 01-31-2012, 05:34 PM   #2
mikeythejew
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Vehicle:
07' wrx
Mothballed until winter

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I suggest taking your cat off and cleaning it. Drop it in a dog tub full of ERA laundry detergent and hot water and let it soak for a day.
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Old 02-01-2012, 02:23 AM   #3
Uncle Scotty
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OK Houston
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you tell us NOTHING about the car

not what car it is
not how many miles on it
not about mods

nothing


how are we supposed to help??
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Old 02-01-2012, 05:44 PM   #4
RolySaul
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Sorry Scotty, I know better and I apologise.

The car is an '07 Wagon "i", with no mods, 143,000 K on it, standard, runs like a top other than this intermittent problem.

It's black on the very bottom 1/4 inch of the circumference of the tailpipe tip, but not enough to turn your finger black, if that helps any. I rub my index finger on it and it comes away clean, so it's not a tarry gunk or anything .

When it idles, I can squat behind the car and sniff the exhaust and I never smell any rotten eggs or see any blackness, the exhaust "seems" perfectly normal to every other in my limited experience.

Speaking of idle, it idles great, but very occasionally, even if warmed up, it will run at 1,000 rpm's steady for a minute, then drop to 700 rpm's for 5 minutes, then repeat. I mean both speeds it runs like a champ, but there's a definite "switch" happening.

Looked thru a bunch of threads here, one of which was mine and you gave advice on, (thanks again), and have come to the conclusion that I have a mixture problem, occasionally (and suddenly it seems) running rich enough to defeat the Cat converter front/back ratios on the sensors and pop up with p0420.

I am hopeful that the cat is not necessarily bad especially if the motor generally runs really good, but the fact that the problem is really intermittent inches me along to the conclusion that the problem is "switching" on and off as if there's a sensor going...

I'm just trying to think it thru with your help seeing as how I can't work on it myself until spring, and I'm willing to gamble on the garage doing the front sensor if it prevents me from shelling out for a new cat. If I lose that gamble, well sucks to be me but it's not the end of the world.

Also I'd like to fix the fuel ratio problem before i put in a new cat then trash that too.......anyways thanks for helping, Scotty, I'll try to be more clear in the future.
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Old 02-01-2012, 09:52 PM   #5
Uncle Scotty
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try some techron fuel system cleaner
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Old 02-02-2012, 08:35 PM   #6
REDrexsti
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Join Date: May 2011
Location: Fort Dodge
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2004 wrx
jbp

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Usually a plugged exhaust will get worse as the car warms up. Borrow a scan tool from a friend, or maybe take it to a shop to see what kind of reading you are getting from the o2 sensors. +1 for giving the injector cleaner a go.
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Old 02-03-2012, 03:59 PM   #7
ManualOverAuto
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2001 Impreza L coupe
Sedona red Pearl

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My car (01 impreza coupe) has the same code. I was told by a mechanic that I need a new cat. Who knows if I actually do or not. I have smelled the rotten egg smell though, and I do get horrible gas mileage (19 mpg). When the light is off I get back to like 25 mpg though. The light switches on an off. Usually staying on longer than it stays off.

Worst case scenario would be that it's a head gasket leak, and it's burning oil that is building up on the sensors giving them a bad reading. I doubt it's that because I haven't noticed a loss of oil. Prolly just a bad cat or sensor.
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Old 02-04-2012, 07:20 AM   #8
RolySaul
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Thanks for the help guys, Ima take it in next week and get a new front sensor, if that doesn't help then I'll re-think it.

Actually, I'll try the fuel system cleaner first, ya never know it might be that simple.
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