sigh.. CEL

[stateofidleness]

checked and "cleaned" the MAF yesterday and it looked brand new. car is running top notch. go to start it this morning and minor hunt at idle again. last 3 cold starts were perfect, no hesitation or hunt at all.

half way to work, CEL comes back on (after 3 days of solid driving). Car is running great though.

so I guess my next step is to have the Air Change-over valve and the Electronic Change-over valve replaced.

I had read elsewhere that the Tiptronic models have an extra vacuum valve or something that can also go bad... since it requires taking the alternator out to replace these, I want to replace as much as possible all at once.

what can i expect to pay in labor? and should i replace the seconday air system hoses as well?

[Daniel R]

I have had all the same fun and games you are describing with my 2000S. It turned out to be an MAF on the way out and a pair of oxygen sensors in a really bad way, one so bad that that bank was bringing up misfire codes. When I replaced both the MAF and O2 sensors it was back to normal.

On a side note, if your car has been doing this for some time you may want to check the catalysts for damage. I switched to bypass pipes when I replaced the sensors as it was a less expensive option than new cats. I am now catless, as in Australia we only have to run one set of cats so the Boxsters only have the main cats and one set of O2 sensors.

Good luck.

[stateofidleness]

this all started within about a month.
tonight on the way home from work, i threw another code (only 1 this time)
p1128 which looks like a rich threshold on banks 1-3

i'm suspecting some kind of vacuum leak at this point but will have to dive in tomorrow morning. how does a "driveway mechanic" spot a vacuum leak? any tricks?

i was all ready to just have my air changeover valve and ECO valve replaced, but this code might indicate something different. I scoured the net, but haven't found too many people with just the ONE code, many had the accompanying 1130 code. What does having one code indicate?

*thanks for all the help and suggestions, hopefully i'll get her running top notch again soon*

[Bladecutter]

Originally Posted by stateofidleness

this all started within about a month.
tonight on the way home from work, i threw another code (only 1 this time)
p1128 which looks like a rich threshold on banks 1-3

I believe if you look for a vacuum leak, you will be looking in the wrong direction.
I believe that this code is going to point more in the direction of the two O2 sensors on that bank of the exhaust going bad.

When the exhaust passes through the headers and past the O2 sensors, the computer receives a signal that tells it if there is or isn't alot of Oxygen in the exhaust. If there's too much Oxygen, then the computer richens up the mixture. If there's too little, then the computer leans out the mixture.

Right now, the O2 sensors are saying that the one bank is running too lean, and the computer can't richen up the mixture for that bank any more than it already has, hence the CEL being lit.

If you replace those two O2 sensors, that will most likely resolve the issue.

Some recommend just replacing all 4 at the same time for the best results.

BC.

[stateofidleness]

consensus seems to be that it is the O2 sensors that are REPORTING the problem, but are NOT the problem. They don't really affect the mixture, they just report it.

[Bladecutter]

Originally Posted by stateofidleness

consensus seems to be that it is the O2 sensors that are REPORTING the problem, but are NOT the problem. They don't really affect the mixture, they just report it.

You're most likely going to find out that your impression is incorrect.

If the sensors are faulty, then they will send the wrong signal to the computer, which causes the computer to richen the mixture.

Here, try this:

Switch the O2 sensors from the left exhaust to the right exhaust, and vice-versa.
If the problem follows the O2 sensors, then my suggestion is correct.

If the problem stays with the bank, then you are on the correct path.

It won't cost you anything more than about an hour's time to swap the sensors, and a day to drive the car around.

BC.

[stateofidleness]

sounds logical. i'll give that a try! googling some more and I keep coming across people stating the MAF.. yada yada... When I looked at mine, it looked BRAND NEW! Does a failed/failing MAF have any visible signs of failure or do they just "not work" after some point? also, during reinstall of it, could that have introduced a vacuum leak where it connects? I've read that if you get BOTH codes, it is most likely the MAF, one code and it means something is wrong on that side... (might go along with the 02 sensor theory, but i haven't had ANY indicators up to this point that an O2 was on the way out)

Also, and this may be far-fetched, but I have been using 92 octane (Valero) gas for the past few weeks only because my Shell (only 93 octane in town) is not on my daily route. Could this cause some kind of lean issue as well?

Would filling up with 93 and maybe some additive do anything for me?