bornrich

A little over a week ago I installed a K&N CAI ( yea, yea , I know). Soon afterword I got the CEL. I read the codes and it was P1128 and P1130. I checked all the connections, reset the CEL and just a few miles later the CEL is back with the same codes. I then removed the MAF and cleaned using MAF sensor cleaner. The CEL appeared again. I then re-installed the stock air-box and reset the codes. Out for a drive today the CEL is back. Also cleaning the MAF I just sprayed the cleaner at the opening at the bottom.

I guess it is time for a new MAF.
It is just strange to me this occurred after the K&N install. NOTE: I did not oil the filter prior to the install and the kit was new.

Macster

Why oh why do Porsche owners want to mess with a very good filtration system is beyond me.

Ok. Deep breath. Relax.

Ok, it might be time for a new MAF. But maybe not.

The cause of the CEL and error codes could just be a leaking oil filler tube cap. A leaking cap had me (mis)diagnose a MAF and replace a perfectly working MAF with a new and very expensive MAF.

When with the new MAF in place the error codes came back shortly thereafter the oil filler tube cap was found (heard) to be leaking.

(The good news is when the replacement MAF finally died -- no mistake this time it was bad -- the old MAF dug out of its box in the storage closet installed back in the car worked just fine and continues to work just fine to this day.)

Anyhow, with the engine idling check the cap wiggle the cap around while listening carefully for any leaks.

Now the 996 of course has the engine exposed -- compared to my Boxster which of course has the engine buried amidships -- so you'll get more background noise which might tend to drown out any slight hiss of a leaking cap so pay attention too to if the engine reacts as you move the cap about. If it does...

Leaky cap or possibly a leaky oil filler tube (or a cracked one).

If the cap is not leaking.... well, we can talk again.

Sincerely,

Macster.

bornrich

The oil filler cap and tube are sealed. No cracks in the tube and the cap is securely tightened. With the cap off there is gentle suction.

Macster

Might be the MAF. I hate to have you replace it on just my suspicions though. Expensive lessen if it is not the MAF. And I offer no guarantee so if you run screaming from your PC to a qualified Porsche repair shop for a professional's diagnosis my feelings would not be hurt in the least.

Anyhow, I have to suggest you double check the K&N installation to make sure there are no air leaks. Even if they are before the MAF this can allow hot air into the intake which can affect the MAF. Also, this can disrupt the laminar air flow that is critical to the MAF's proper function.

You could even go so far as to remove the K&N and installl the stock air filter/air box.

If all is well, a cheap trick is to disconnect the MAF, clear the codes to reset the long term fuel trims for one thing then drive the car and see if the error codes come back. Be sure you drive the car enough to give the DME plenty of time to detect the conditions that trigger the error codes. Once aroiund the block ain't nearly enough.

15 or more miles to ideally follow a reasonably close approximation of the drive cycle that the DME likes so it can cycle through a whole bunch of tests of the various monitors (sensors, misfires, converters, evap, secondary air, etc.).

Sincerely,

Macster.

bornrich

If you read my original post I did remove the K&N and reinstall the stock air box. Reset the codes and the CEL came on again in about 35 miles. So you are suggesting I unplug the MAF after clearing the codes and drive the car for a while and see if the codes return. If they do, then that confirms that the MAF is faulty?

Macster

Sorry missed that part of your original post.

Before you unplug the MAF you cleaned it if I remember correctly? Did you clean it with proper MAF cleaner? Just asking. If you cleaned it with something that leaves a residue...

A shade tree mechanic's technique is to disconnect the MAF, clear the codes to force the DME to unlearn what it learned based on input from a possible bad MAF then drive the car and see if the CEL comes back on and error codes come back.

You have to be aware that the CEL can come on at some point because the MAF is no connected. So if the CEL comes on you can read the codes to see if they are the same error codes or different ones or a combination. However, when I tried this -- when attempting to trouble-shoot symptoms that were at that time unbeknownst to me coming from a failing AOS -- the CEL didn't come on.

If you drive a reasonable drive cycle and the CEL doesn't come on then you reconnect the MAF and clear the codes again -- to reset the DME's learned behavior back to the factory defaults -- and see if the codes come back.

Yet another technique is to monitor various data like short term fuel trims. Now I did this when what proved to be the replacement MAF was acting up but I do not recall recall the short trim behavior now. I seem to recall it was like rail to rail. I do know the short term trims were behaving in a way I never saw them behave before and I observed them over some period of time off and on using an OBD2 code reader/data viewer.

A word of warning: After you clear the codes the DME will go through a serious learning phase and the trims can swing from negative to positive and back and forth quite a bit but the swings should become less and less as the DME well learns what the proper fueling is and adjusts the long term trims.

Roughly a few points plus or minus is about all you should see. When an adjustment approaches +/- 10% that's about the time a CEL can appear.

A dealer would have course the proper diagnostics computer equipment that could query for info that would more clearly point to the MAF or something else. Thus the MAF could be confirmed or eliminated quite quickly.

Sincerely,

Macster.

Shark Attack

and another thing is everyone always runs right for the MAF.

OMG I got a CEL must be the MAF.

C4CRNA

"Also cleaning the MAF I just sprayed the cleaner at the opening at the bottom."


Take it out completely and spay a half a can of cleaner all over, in, thru, and around the MAF
then reinstall

Macster

The MAF does come under suspicion first in cases where it really belongs further down on the list of suspects. Part of the reason is it is easy to get to. And doing something with it makes one feel like he's doing something. Otherwise most of us can only stare at the car wondering what the heck to do, what's wrong.

However, in this case to the OP''s credit the error codes do point to a MAF problem.

For instance for my 996 (Turbo) a P1128 error code is Oxygen Sensing Adaptation, idle range, bank 1 below limit.

The 1st item under the list of possible fault causes is "Incorrect signal from MAF."

Next is "fuel pressure too high" followed by "fuel injector leaking" followed by "EVAP canister purge valve open".

That both P1128/P1130 were present means both banks are manifesting the same problem.

This points to a common failure. MAF is certainly common to both banks, as is fuel pressure and EVAP canister purge valve open. It would be less likely both banks had one or more leaking injectors.

If MAF can be eliminated then that leaves fuel pressure, EVAP purge valve, leaking injectors.

If MAF is not the cause, and other more exotic farfetched things can be eliminated (like a leaking oil tube filler cap) are eliminated, my money is on the EVAP purge valve.

Or... AOS. My Boxster's 2nd AOS as it was failing on a drive across the western USA would as I would pull off the freeway and sit at a light on the off-ramp would trigger the CEL with P1128/P1130 error codes. I remember thinking at the time no real big deal for it was the MAF and in a pinch I could disconnect it and manage until I could get to a dealer and buy a new one.

Well, it proved to not be the MAF but a bad AOS that made its badness perfectly clear with a huge continuous billowing cloud of oil smoke upon start up the 3rd day out on the road.

Sincerely,

Macster.

bornrich

No everyone does this as we are directed to possible problems via the code(s) that are supplied by a code reader. Now if anyone, and I have not seen this, ever just relies on the CEL light alone for a MAF failure diagnoses that is just plain dumb.

In my case I did the research but I wanted to be sure before I wet and spent the money on a new MAF.

bornrich

I found that there was a hole in a vacuum line to my brake booster. I hope this is the final solution. Seems strange that this failed while I installed my K&N though. Well at least I have a backup MAF now.