mumeh

From what i can deduce, the MAF on the 996 is a consumable item at some point. My car is a 99 also and had this problem when the mileage was in the teens but the car was 5-6 years old. My $0.02. Martin

I'd go with a different sub, possibly this one Iyse, I think telly808 is right on the money here (getting a sub with minimal installation depth), but I would add a few points: 1. If at all possible, DO NOT CUT THE CAR. The subsequent reduction in resale value is large and immediate. Take a hard look at spending some extra effort fabricating an enclosure instead that will be removeable. I know others have done this in a Boxster before. Since it is not roomy back there, you will need a shallow subwoofer and a very custom box. I suggest going here for some examples of a similar problem (different car) solved with a custom enclosure. 2. I have not tried the Pioneer unit, but I am using an Audiobahn 12" (see this eBay ad) woofer in my 996 (yes, I fiberglassed it myself) that is very shallow also, and it has the advantage of power handling, lower F3, and MUCH greater excursion. I believe there is a 10" version also, which will better fit the 986 size envelope. 3. In addition to maintaining better resale value in your car, there is one other reason to fabricate an enclosure, and that is that you can take advantage of the better and more predictable characteristics of a sealed box. Just my $0.02. Hope this helps.

Izzy, Hope I can help here. I did indeed replace both the MAF and the O2 sensor for banks 1-3. The difference is that, for me, the P1123 code did not actually lead me to the real probem right away. I replaced the O2 sensor first, and the CEL was quickly back on again, indication that the O2 sensor was, at best, not the sole source of the problem, and likely was in perfect shape. What I have learned from my experience and the many other posts here is that the P codes give you hints as to the normal operating parameters that are being exceeded, but they do not always point you directly to the source of the problem. That said, it sounds like you may have a different problem, since you already have a brand new MAF. My experience with other cars tells me that oxygen sensors are a good first place to look for things like this (especially after 50K+ miles), and since this sensor is not horribly expensive and it is easy to replace on the 996 (no more than 15 minutes, including jacking the car for better access and hand-washing), this should probably be your next move. If it makes you feel any better, rest assured that, given your error code and the history of the car, this is the FIRST thing any mechanic would look at with a P1123. With the MAF on my car, I hesitated after first replacing the O2 sensor because I did not want to "throw good money after bad," but in the end since I have replaced it, all my CEL problems have gone away and I am back to driving the car with confidence in its reliability. Easily worth the price. Hope this helps. Martin

In my experiance (virtually zero with generic scan tools), I have never seen a air mass reading that low, ever. Perhaps again this is just something that generic scan tools display differently than the PST2/PIWIS. Either way, the car is getting MORE air than it thinks it is as the fuel trim is in the plus. In that case, here is my question to you. If you state that 25% is the threshold for LTFT, then why does he have a check engine light and his LTFT is at 9%? I disagree. The car is having to add fuel. Look at his LTFT number, its positive. The o2 sensor is reporting a lean a/f mixture and the DME is trying to adapt by adding fuel, hence the positive LTFT number. Exactly. If the air mass sensor only reports 5 gm/s of air flowing into the engine, its only going to inject enough fuel to burn 5 gms of air. If the air mass sensor is defective and reading low, there is going to more air going into the engine than it thinks. The mixture will be lean, the o2 sensor will report this, the DME will add fuel up to its threshold, and the CEL comes on. P1123 and P1125 are the LEAN threshold, the car is too LEAN for the DME to adapt. If he had any of those problems his fuel trim numbers would be negative, as the DME would be subtracting fuel to compensate for the extra fuel that a bad evap valve, leaking fuel injector, or too high of fuel pressure would deliver. The fact this his fuel trim numbers are positive screams either bad maf or vacuum leak. Thats my two cents. I wanted to close the loop here on the orginal problem. I checked a lot of different things, and after finally checking for vacuum leaks I took the plunge and bought a new MAF sensor. I have waited about three weeks and driven the car quite a bit, and no CEL. Also, throttle response is improved. The car has never made it more than a few days with a CEL after a reset. I consider this problem SOLVED. Thanks to everyone who chimed in, and I hope that my trials and tribulations might help someone else with similar problems. Thanks again, everyone!

That's funny. I have actually had the same problem with the Fastrak system in California. It works just fine on my other car, but doesn't work on my 996 no matter where I place it on the windshield. Hanging it out the window works fine. I thought it was just me.

I owe everybody here a big THANK YOU for their input. I was not able to tinker with the car for a while, and I suffered bigger problems than the CEL, as my battery was starting to go south. I looked at this battery/alternator problem for a bit (charging with a charger, observing behavior, etc.) and then just decided to take the plunge and get a new battery. Not only was my battery problem solved, but lo and behold, no CEL! I drove the car with no CEL for weeks, and thought that I had solved the problem. I began to view myself as "Master of the Technical Universe." Why, my arm was almost getting sore from patting myself on the back! I thought about writing a post here about the value of keeping an open mind when troubleshooting complex systems, and how many of us fall into the trap of assuming certain problems to be more technical than they really are, blah, blah, blah. Happy to have a car with no CEL and problem resolved, right? Wrong. CEL just went on again after a month or so of light driving. Yep, P1123. I guess I'll disassemble the entire car now looking for the mythical evap canister (maybe it will be filled with magic candy!) now based on Loren's diagram (thank you Loren). Drats. I've been humbled, and my "Master of the Technical Universe" title has been ripped from me, and alas, now I am just a guy with car with a glowing CEL. Fame is indeed fleeting. Back to square one. As usual, advice welcome.

Thanks for the help. I will gather this data and report back. It may take me a week or so, as I don't drive the car much during the week. Unfortunately my software does NOT let me snapshot sensor data during the CEL trigger, so we'll just have to rely on the static information. And yes, the car is bone stock.

Well, as the guy who started this thread, I would be remiss in my duties if I did not thank everyone for this wealth of information, as I am learning a TON about the closed loop operation of these engines. Everyone has taken great pains to make their points in a way that the common man can understand, and these discussions actually make sense to me. While I remain frustrated about my inability to solve this problem, I AM getting a lot of information and know more about this car than I did. Putting aside the lean vs. rich argument for a moment, can anyone chime in the troubleshooting sequence I have put together? 1. Disconnect battery for extended period of time to reset internal engine parameters. This is cheap and easy to do, and should do no harm. 2. Check evap cannister circuit and make sure that everything seals nicely. Again, cheap and easy. 3. Replace MAF Sensor. The fact that first Bank 1 and then Bank 2 showed error codes makes me suspicious that leaky injectors are not the most likely cause. For the longest time, I just received Bank 1 errors, and only recently did I start to see Bank 2. 4. Look into injectors. Ouch! Suggestions?

Funny this. I replaced the O2 sensor, reset the error code AGAIN and for a while the problem appeared to be gone, but later the CEL recurred and now I get both P1123 and P1125. My scan tool is able to detect multiple codes. My hat is off to Porsche for consistency between the 996 and Boxster emission systems, but other than that I am irritated and perplexed. Where do I go from here? My idle is quite steady and engine performance appears to be very strong. I just have that darn CEL light on quite regularly. As mentioned before, I am loathe to approach the dealer unless I think that they can solve the problem any faster.

I replaced the O2 sensor, and after some hours of operation, the CEL came back on, with the P1123 error again. Should I be looking at leaky injectors now? Any advice helpful.

Good advice, and thanx for the help. I have the sensor on order as we speak. I will post the results here once I get it in hand.

I was unable to get a sensor snapshot of the engine readings when the error code occurred, but I have been able to verify that it is only the P1123 that is tripping the CEL. I have attached the fuel trim settings per your instructions. They show about 30 seconds of idle, peppered by one or two engine revs just to see the difference. Thanx again for your help. I am approaching a smog test in CA, so you can imagine why I want this resolved particularly quickly. Any help is appreciated.

Addendum: The CEL has gone on again. If this piece of information helps, it always seems to go on when I am stuck in traffic, idling for long periods of time.

After resetting the CEL, I finally (again) got a CEL signal, and it is P1123 again. I did go in and look at the characteristic of the O2 sensor, and it DOES indeed vary rapidly between the two threshold voltages you mentioned. I still have not observed a P1125 error, and the RPM is at 700 steady. I have attached my MAF readings obtained via the Digimoto unit used to monitor OBD II. Any suggestions for how I might go about narrowing the problem? I DID try dipping the MAF in isopropyl alcohol and replacing, to no avail.......