Advice for CEL coded P1128 & P1130

[heyjae]

Originally Posted by 2000SoCalBoxsterS

But my question is, why does the actual code definition say it involves my O2 sensors? Should I replace all four of my O2 sensors? I hear they are about $130 a piece.

The O2 sensors are just reporting the symptoms of the problem. Since they are the last sensor, there is so much upstream that could result in a O2 code. Cleaning the MAF may work, but if it doesn't, look for vacuum leaks. A vacuum leak could cause a rich condition. In addition to checking the usual tubing around the motor, check the oil cap, oil filler tube and oil dip stick. If that doesn't work, get a new MAF. Keep in mind there are 2 versions. It could be the air/oil separator, too. It's doubtful both O2 sensors went bad at the same time, but stranger things have happened--I recently replaced my O2 sensors and one replacement was bad from day 1 and it took forever to figure that out. Or take it to a shop and have them diagnose. These kinds of problems can take a ton of time to figure out without the proper diagnostic tools.

[2000SoCalBoxsterS]

Originally Posted by heyjae

The O2 sensors are just reporting the symptoms of the problem. Since they are the last sensor, there is so much upstream that could result in a O2 code. Cleaning the MAF may work, but if it doesn't, look for vacuum leaks. A vacuum leak could cause a rich condition. In addition to checking the usual tubing around the motor, check the oil cap, oil filler tube and oil dip stick. If that doesn't work, get a new MAF. Keep in mind there are 2 versions. It could be the air/oil separator, too. It's doubtful both O2 sensors went bad at the same time, but stranger things have happened--I recently replaced my O2 sensors and one replacement was bad from day 1 and it took forever to figure that out. Or take it to a shop and have them diagnose. These kinds of problems can take a ton of time to figure out without the proper diagnostic tools.

Thanks Heyjae, all good advice but please don't make me open up that mid-engine compartment again to look for the vacuum leak. 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.

[Gary in BR]

Heyjay:
How about posting a few pictures of the Boxster, in your signature it reads like it must be on mean Box.

Can someone explain exactly what happens with a dirty MAF?

[2000SoCalBoxsterS]

HeyJae, specifically which of all these rubber tubes are vacuum lines? Which ones should I check?

[chris hankins]

I just had the same codes pop up (1128, 1130) as socal2000, and I'm starting with cleaning the MAF thing and looking at the oil cap, other obvious vacuum leaks. @ questions:
1. Is there any real danger in driving my car while I get this thing figured out (note that I generally drive the car as it was intended, but am willing to back off in the short term)?
2. This is probably a stupid question, but after I clean the MAF, should I reset/clear the codes, or will the CEL just go off after a successful fix?

[2000SoCalBoxsterS]

I have now driven about 250 miles since I cleaned my MAF and changed my air filter and no CEL.

I have read on the PCA.org Q&A tech section that long term driving with your fuel air mixture being too lean or too rich due to a bad or dirty MAF can cause damage in that if it is too rich it can burn out your CATs.

I cleared my CEL with a code reader. I don't think the CEL will clear itself simply because the cause has been resolved.

[AUDIOGUY]

I cleaned my MAF and cleaned and re-oiled my EVO filter this weekend... car definately runs better. Smoother idle and no bogging out. CEL is back on now though. I may have a bad 02 sensor somewhere??

Who knows. I am not into going to have it looked at by a pro right now. I have a
feeling they wont know any more than myself.

[skip_168]

Originally Posted by chris hankins

I just had the same codes pop up (1128, 1130) as socal2000, and I'm starting with cleaning the MAF thing and looking at the oil cap, other obvious vacuum leaks. @ questions:
1. Is there any real danger in driving my car while I get this thing figured out (note that I generally drive the car as it was intended, but am willing to back off in the short term)?
2. This is probably a stupid question, but after I clean the MAF, should I reset/clear the codes, or will the CEL just go off after a successful fix?

It took me about a year with the CEL light on & off to finally get around to fixing it, and no damage occured.. not really a big deal, as long as you know what the codes are..

Yes you should clear the codes out after any repair. The ecu will turn it off if the code doesn't reset, but it takes like 500 key cycles or something like that..

[heyjae]

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.

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.

[2000SoCalBoxsterS]

Originally Posted by heyjae

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.

Hey HeyJae, thank you for taking the trouble to write such an extensive response. But this is a little over my head though in terms or seeing the values for the MAF /Intake.

My code reader is very basic. All it said was P1128 & P1130. This was with the ignition on and the engine not running. There is another function on it where you do a "MIL" reading and it says for that you have the engine running. But even if I then saw these various values I wouldn't know what to do with them.

[joyfrog]

I had these same codes about 6 months ago I tried the MAF cleaning first.....to no avail then I tried something really stupid.....atleast I thought......I bought a new oil cap......FIXED!

[skip_168]

My theory on how the MAF sensor cleaning cures the code 1128 & 1130 is pretty simple.. the element,( the paper clip lookin' thingy..), sits in the intake air flow..

the MAF sensor is an accurate current source device in its simplist terms.. the sensor sends a current through the element which generates heat.. now as air flows over the element, it removes heat from the element which causes an increase in current to maintain the element temperature.. more air = more current..

The ECM uses the current measurement to calculate the air flow into the engine.

What I think happens to the MAF is it gets a coating of dirt, the contaminate acts as an insulator.. once it gets thick enough, it skews the airflow measurement, in other words, the element does not see all the airflow.. the result is a reading of lower airflow reaching the ECM, which injects a less fuel than actually needed.. thus runs lean...

just an engineering guess....

[2000SoCalBoxsterS]

Originally Posted by skip_168

My theory on how the MAF sensor cleaning cures the code 1128 & 1130 is pretty simple.. the element,( the paper clip lookin' thingy..), sits in the intake air flow..

the MAF sensor is an accurate current source device in its simplist terms.. the sensor sends a current through the element which generates heat.. now as air flows over the element, it removes heat from the element which causes an increase in current to maintain the element temperature.. more air = more current..

The ECM uses the current measurement to calculate the air flow into the engine.

What I think happens to the MAF is it gets a coating of dirt, the contaminate acts as an insulator.. once it gets thick enough, it skews the airflow measurement, in other words, the element does not see all the airflow.. the result is a reading of lower airflow reaching the ECM, which injects a less fuel than actually needed.. thus runs lean...

just an engineering guess....

Great explanation. But my codes P1128 & P1130 indicate a overly Rich fuel condition.

[mikesz]

A new oil cap? I like that idea!

[mikesz]

Finally got a nice weekend in RI. Replaced the rear brakes, rotors, pads, sensors then went digging for the motor. Took out the air filter, it literally disintegrated as I was pulling it out. I have never seen an air filter so bad in all my life. I got my shop vac and vacuumed the cleaner box and put the new filter in. While I was in there took out the MAF and cleaned that also. Put everything back together, reset the CEL and drove around the Scituate reservoir for 90 miles and no CEL so tomorrow I take it to be inspected.