58ceramicgreen

Hi guys..have a technical question for the pro's. Think I know the answer but wanted to run my thoughts past the experts first.
Out for a drive the other day, about 40 mins into the cruise the car starts to hesitate, this is at highway speed. When I come up to a set of lights, depress the clutch the car dies. Fires back up but hunts for an idle. I get to my destination, about 20 mins later it's time to try and make it home. Runs fine at first than again about 1/2 hour into drive the car starts to stumble again.
No check engine light the entire time. I don't have a durametric but I do have an obd scan tool. I pull codes p0103, p1127, p1129 and p0112.
I pull the maf, clean it, unhook the battery to reset everything and all good again.
Today I took the car for a coffee, all good. When I get home I let it idle in the drive way and it's hunting all over, dips, revs up, dips and eventually stalled.
Last Sept I replaced the maf with a $40 eBay Chinese knock off, car ran perfectly for the last 4000 kms. I unplugged the Maf and started the car, won't idle at all. Plugged back in idles but hunts. Thought I would try the old Bosche maf again, won't even idle.
So..back to the Chinese maf,cleaned again, idles ok for a bit then hunts.
I'm thinking the old saying pay once now or twice later applies here, maybe should have just bought the bosche one right from the start?
I can't find any vac leaks by ear or by spraying throttle body cleaner around all the hoses listening for the tell tale increase in rpm. When I pull the oil cap at operating temp the idle surges up so I think the AOS is ok. I know the codes I posted above are maf and o2 sensor related but I have a feeling the maf is the culprit again.
Anyone have any thoughts or guidance?

Macster

P0103 - Mass Air Flow Sensor - Above Upper Limit.
P0112 - Intake Air Temperature Sensor - Below Lower Limit.
P1127 - Oxygen Sensing Adaptation Area 2 (Cylinders 1 - 3) - Lean Threshold.
P1129 - Oxygen Sensing Adaptation Area 2 (Cylinders 4 - 6) - Lean Threshold.

I think the key is the 1st two error codes.

The 1st two certainly point to the MAF.

Couple of things. 1) Have you tried clearing the codes and just unplugging the MAF? Leave it in the intake but disconnect it at the wiring harness.

2) Check the oil filler tube cap carefully. With the engine idling check very carefully for any sounds of an air leak at the oil tube filler cap and wiggle the cap and see if you can create an air leak this way.

(I replaced a perfectly good MAF when the real problem was an air leak at the oil filler tube cap.)

If you do need a new MAF, IIRC for the early Boxsters there was a MAF update. The original part is no longer available from dealers.

The new MAF requires a DME software upgrade to work. I do not know how much this costs.

So, if you buy a replacement MAF you have to be sure you get the right one for your car.

58ceramicgreen

Thanks for the tips. I pulled the connection plug off the maf while there were no codes and it didnt want to idle, just stalled out. Granted I didn't try driving with it unplugged to see if it would smooth out. It did throw a code with the maf unplugged obviously but no mil.
I just went out checked the oil filler tube and cap. All seem good and tight. If I pull out the dipstick or unscrew the oil fill cap the revs jump from around 750-800 up to about 1000rpm. (I believe this is normal? Should be under vacuum?)
I know there was a change in maf part numbers, it's the Bosch 996.606.123.00 part number I'm after, I'd rather skip the dme reflash and upgraded maf if possible. I suspect my problem is the knock off $40 eBay maf..really should have bought the Genuine Bosch from the get go.

Macster

The usual order of steps is to disconnect the MAF, clear the error codes which even if there are none active resets all the learned fuel trims, etc. to their defaults. Then start the engine and see how it works.

The results you posted suggest the problem doesn't lie with the MAF but the question isn't settled by any stretch of the imagination.

But given the behavior of the engine I would be reluctant to suggest you repeat the test and give the engine and DME time to adapt to the absence of the MAF and the reset of all the learned values.

While I have removed the dipstick and even the oil tube filler cap from my Boxster many times I do not recall the rpms jumping that much. The engine reacts to be sure, as the removed dipstick, or cap -- especially the cap -- is a huge and sudden intake air leak or vacuum leak.

(If it wasn't so blasted hot outside I'd go out and repeat this to refresh my memory.)

But a healthy engine and a properly working engine controller with a working population of sensors should be able to adapt and recover in just moments.

'course when you replace the items removed the engine has to adapt to the sudden absence of the huge intake air leak.

Now the cap has leaked in my car. For other owners a leak is the oil filler tube. It cracks and leaks under some conditions. Be sure you eliminate the tube as a possible intake air leak.

But the error codes do not suggest an intake air leak but just the opposite. The engine is possibly running too rich.

For PO103 a bad MAF is near the top of the list of possible causes.

For P0112 this points to the intake air temperature sensor which is part of the MAF's function. If there is a fault a default value of 60C (IIRC) is used so if you have an OBD2 code reader/data viewer and you observe intake air temp and it is at 60C when all this is going on...

For P1127 top of the list is incorrect signal from the MAF. Yet another possible fault fuel pressure too high or a leaking fuel injector or last an EVAP canister purge value open. But you read no error codes pointing to the tank vent/evap system.

Note then two possible faults indicate there is too much fuel. In fact the error code texts both state "lean threshold". IOWs, the DME has gone as far as it can to remove/subtract fuel only to reach its limits.

My only reference here at home does not list P1129, but since it refers to the other bank the same fault causes have to apply.

Mix the above in a bowl and toss in the fact the engine rpms climb when extra air is added -- instead of remaining the same or even falling -- suggests there is too much fuel.

Not enough perhaps to condemn the MAF but getting closer wouldn't you agree?

58ceramicgreen

Thank you Macster!! You're a wealth of knowledge!! I'll post back some results after some more troubleshooting!

58ceramicgreen

Ok..quick update for you Macster.
Checked and rechecked for any sort of vacuum leak, can't find anything.
Pulled off the MAF connection, disconnected the battery to clear everything and went for a drive.
Car is running perfectly, idles great, no hesitation, check engine came on obviously. Codes are P0102 and P0112 (both MAF related I believe?) I've only driven about 25kms (15 miles)
So..based on this, safe deduction to needing a new MAF? Am I that lucky? (by lucky I mean a $250 part I can easily replace myself in under 5 mins!!)

Macster

Ideally you would want to drive the car until all the readiness monitors were complete, save any that might be held up due to the MAF being out of the picture.

This might be 15 miles but it can be longer. I'd consider around 30 miles a nice round number. When I was going after a troublesome O2 sensor problem the CEL would come on after about 30 miles of driving, not before. A real bear to catch the sensor actually acting up. And around the same number of miles when what proved to be a leaking oil filler tube cap was causing me grief. 30 miles happens to be my work commute distance, too. But I'd just about get home and the CEL would come on.

Also, after you're sure the problems/error codes do not reappear with the MAF out of the picture, repeat the test this time with the MAF (back) in the picture and confirm the symptoms/error codes come back.

Absent the right tools and equipment to check out the MAF (and eliminate other things) in the service bay you have to work at this.

58ceramicgreen

Just to add some closure to this thread incase anyone ion the future has the same issues or codes..
I ran the car with the unhooked MAF for a few days, totalling about 150kms. ran perfectly. (with check engine light and the two codes P0102 and P0112. No other codes popped back up.
I re-hooked the maf back up and it ran like crap again..hesitation, rough idle, died etc. At this point I'm 99% sure it was the maf.
ast Friday, dropeed in a new Bosch unit..car is running like adream, threw another 200+kms on the car over the weekend and hasnt skipped a beat.
It's amazing how much trouble one little piece of plastic can cause!

Boxed 896

I have a 1998 Boxster that is giving off codes P1124 and P1126 (running lean codes) I took the car to Porsche and it was determined that the car doesn't have any vacuum leaks, and all of the O2 sensors are working correctly. The problem is the car will not pass NY emissions inspection due to the computer is in Not Ready for just the O2 test. The dealer told me that Ambient Pressure Sensor that is non replaceable due to it's in the DME is the problem and I would have to replace the DME. They said my Ambient Pressure Value is 855 and it should be over 1000. Is it possible that the MAF Sensor is the problem and not the DME? I can't find anyone who has had this issue.

Macster

There is an ambient pressure sensor and it is part of the DME.

However, if this was bad I would expect a P0105, P0106, P0107, P0108 or P0109 error code (or some combination of codes). (And my limited knowledge is the engine should run lousy.)

Unless the dealer didn't provide you with all the codes (active and pending) what you do have is:

P1124 is oxygen sensing adaptation range 1 (cyls. 1-3) at enrichment limit.

P1126 is same error for cyls. 4-6.

If DTC P1124 or P1126 logged then fuel/air mixture is too lean.

Possible causes: intake system leak; fuel pressure too low; fuel injectors contaminated; volume supply of fuel pump too low.

Air leak would have to be common to both banks. One possible air leak source is the AOS. When this starts to go bad it subjects the engine crankcase to extremely low pressure which can pull in air and ultimately end up looking like an air leak at the engine. Check AOS hoses and connections for any signs of cracked or broken hoses or connections. With engine idling unscrew and remove oil tube filler cap. If the cap is hard to impossible to remove the AOS is suspect. However, even if the cap comes off with no struggle this doesn't let the AOS off the hook.

While you there, also check that the oil filler tube cap is not leaking. A leaking cap mimiced a failing MAF so perfectly I replaced a $300+ MAF when a $13 cap was all that was needed.

(I've since worn out the replacement cap and had to replace it. I get around 150K miles per cap...)

Assuming the gas tank is not low then you have to check for proper fuel pressure and supply.

You can test fuel pressure at fuel rail test point and remove the fuel pump relay and bridge terminals 30 and 87 (id'd as 3 and 5 on the relay panel) with home made test harness. Fuel pump should operate and pump fuel.

Engine off pressure should be 55 +/- 3psi. Engine running 48 +/- 3psi.

Test pressure ports require new seals. Check with Porsche parts counter guy and get extra ones before you test fuel pressure.

Be careful working around running engine and testing fuel pressure and flow.

But an intake air leak is most often the source of P1124/P1126.

Schnell Gelb

You need an Indie to help with this.
Check all the causes of lean codes - even the stupid ones - like loose spark plugs, missing clips on the plenums/boots. If all else fails to locate the cause of the lean running, suggest a propane test.
An Indie would be the guy to use for a used DME - because he can return it if it doesn't fix the problem.You may have problems trying that ?
Good luck and keep us updated .I suggest you start a separate Thread instead of being a hijacking noob.You'll get more responses.

porker944

I got the same fault codes. Car seemed to lack high rpm power 5500rpm+. I had K&N air filter, and MAF seemed to have an oil drip dried to the film. Tried cleaning the MAF with CRC air sensor cleaner; no effects. Looked at sensor levels with Durametric, did not have any effect whatsoever. I then tested for air leaks, found none, all the seals were tight as a bottle. Bought a new MAF. Problem solved. Replaced K&N filter with OEM filter. Verified this with Durametric, and had the car dynoed, full power again. I hope this helps someone. Thanks.

stl_986

that is why no one ever recommends the k&n oil filters for any car. They do nothing but cause problems.