Hesitation and Surging during WOT

[996noob]

Some history on what had transpired before the problem:

A) Had broken vacuum lines for intake flap switchover and was running without them for a few months.

B) Replaced the vacuum lines, made sure they were connected to the right places.

C) Bought a Durametric to see if I had any codes, cleared them, and there remain no codes anymore for the engine management.

Symptoms:

Only during hard aceleration through the rev band, at WOT, the engine has difficulty climbing revs at certain portions of the rev range. There is no bucking or coughing or sudden loss of power that would cause jerking, but instead the revs just seem to struggle at certain revs, then continue, then struggle again, while the car tries to accelerate up to the red line.

There are no codes from the durametric.

Should I try unplugging the MAF and drive? Will I damage the car if I WOT with the MAF unplugged?

If it drives better without the MAF, does it mean conclusively that the MAF is bad?

What else can I try?

[Loren]

Yes, you can disconnect the MAF for testing. The car will not rev well past 4500 RPM without the MAF (and likely cause a CEL).

Since you have the Durametric software why not look at he idle MAF reading and the 2500 RPM no load MAF readings - if they are not between 12-24 Air mass ML in kg/h at idle and 40-70 Air mass ML in kg/h at 2500 RPM then you likely have a bad MAF.

[996noob]

Yes, you can disconnect the MAF for testing. The car will not rev well past 4500 RPM without the MAF (and likely cause a CEL).

Since you have the Durametric software why not look at he idle MAF reading and the 2500 RPM no load MAF readings - if they are not between 12-24 Air mass ML in kg/h at idle and 40-70 Air mass ML in kg/h at 2500 RPM then you likely have a bad MAF.

At idle, 680 to 720 rpm, the reading was 17.75 kg/h. Holding the engine steady at 2,520rpm, the reading was 49.00 kg/h.

What step should I make next?

------------

Edited with Update - I went down to the car again to try unplugging the MAF. Went for a drive. Had what seemed to be full power restored at WOT!

There are 2 interesting things to note about running without the MAF connected.

1) it did not set off the CEL. But, I think there must be some errors registered if I check it with the Durametric. Will check later.

2) the aircon compressor was not allowed to engage. Re-connecting the MAF allowed the A/C compressor to run properly again. I think this is because running with the MAF disconnected also disconnects the idle control circuit and idle valve, and hence the A/C compressor is not allowed to run, otherwise the car would stall.

Ok, on to conclusions.

Is this a conclusive test that the MAF is on its last legs? Was my 2,520rpm reading of 49.0 kg/h bordering on the low end of the acceptable range and would eventually be off spec at higher rpms?

Do I....

A) try cleaning the MAF with contact cleaner

or

B) don't bother, just buy a new MAF.

Thanks again to the forum, its members, and the search function!

Edited August 5, 2009 by 996noob

[996noob]

Hi Loren,

Your esteemed reply is sought on this matter. Based on my findings, is it sufficient to conclude 100% that the MAF is the culprit to my uneven power at WOT?

Should I then clean the MAF or don't bother and just buy a new MAF?

Thanks!

[Loren]

Why spend $300-$400 on a new MAF if cleaning will work?

Your readings are pretty close so it might just be dirty. Usually a bad MAF will not even change readings when the RPM changes.

Really nothing to lose by trying cleaning - except a few minutes of your time.

[996noob]

Why spend $300-$400 on a new MAF if cleaning will work?

Your readings are pretty close so it might just be dirty. Usually a bad MAF will not even change readings when the RPM changes.

Really nothing to lose by trying cleaning - except a few minutes of your time.

Great. I'll do that and report later.

[996noob]

Why spend $300-$400 on a new MAF if cleaning will work?

Your readings are pretty close so it might just be dirty. Usually a bad MAF will not even change readings when the RPM changes.

Really nothing to lose by trying cleaning - except a few minutes of your time.

Great. I'll do that and report later.

I went ahead and cleaned the MAF a few weeks ago. There was no difference. So I finally decided to order a new MAF despite the airflow readings read by Durametric being within Porsche spec, and no fault codes had been reported by the ECU. I only deduced that a new MAF was needed by using the "unplug-MAF-method" as suggested by forum members. It turns out my MAF was the culprit. The car runs like a rocket again! Imagine that I could not even reach redline in 3rd gear, so the Tip trans couldn't even get me to 4th if I drove at wide open throttle. I am still a little confused as to why this was so. But anyway, it is now solved.

Thanks to everyone who helped me with this.

[wross996TT]

glad you got it working....the MAF is IMHO, the single worst component on the car (not just Porsche). It can fail, become fouled, send wrong signals to the ECU, be easily misdiagnosed, etc. I mean there are times it will throw codes (like PSM and ABS) that have nothing to do with it and other times it won't throw codes at all. Like in my older P-car (where I kept a starter relay in the glove box), I keep a spare MAF around JIC.