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Originally Posted by 2000SoCalBoxsterS
I had read somewhere that if one O2 sensor goes bad it's best to change them all at the same time. I think the reasoning was that whatever fouled the first one probably messed up the others too or the new one will be more sensitive than the older ones and this could cause more CEL problems. My car is 8 years old but I only have 39,000 and change miles on it. Do you think some of the rubber could still have deteriorated just from age? I know the answer to that is probably, but I don't want to hear that. Weather sucks here today so I haven't test driven the car yet to see if my cleaned MAF and new air filter worked.
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It's unlikely that the O2 sensors are at fault here. I've read conflicting accounts about changing just the bad O2 sensor versus changing all of them. Personally, I changed all of mine, but my car has 80,000 miles and they'd be getting close to being replaced anyway and because I changed all of them with generic O2 sensors and I wanted to keep all of them from the same brand. Of course, one of the 4 I got was bad and I needed to replace it right away and bought a different type. It seems to work pretty well so far.
Looking for a vacuum leak and/or troubleshooting codes is a PITA. After checking the low hanging fruit (cleaning the MAF--maybe replacing it, doing a visual on the vacuum tubes, oil filler tube, checking the oil cap), either take the car to a competent shop or invest in some diagnostic tools and resign yourself to spending hours learning and a lot of trial and error. The basic ones to look at are the 2 small plastic tubes coming out of the rubber coupling between manifold and intake plenum/resonator. There's one on each side. I thing the one on the passenger side is visible from the top and the one on the driver side is visible from the bottom. Then there are the rubber tubes coming from the throttle body. But a vacuum leak can be from the air oil separator (maybe), the secondary air injection system (less likely) or even the brake booster (not likely). Unless you are pretty handy, I'd defer troubleshooting those to a mechanic. There's also using propane to check for leaks. Others seem to do it fine, but I've only tried that once and was not successful with that method.
As far as a visual of the MAF before cleaning, it's probably a thin layer of oil or dirt that's causing the problem and it'd be hard to see. If you have a code reader that shows intake flow, mine is about 4-5 grams/sec. Another thing to check is your short term fuel trims. It should be within +/- 10% normally at idle, although it can be as high as +/- 25%. With the code you are throwing, yours is probably +25%. When my MAF was going bad, at idle the flow would jump around and the STFT would be erratic as well, but that's just one data point.