Mass Air Flow and Ox Sensors

A while ago I noticed a slight hesitation with my 2000 Boxster S driving up a steep grade at freeway speed in 5th or 6th gear. Also, occasional hestiation when accelerating. I brought the car to my mechanic who is not a Porsche mechanic but generally very good. The car had a little over 50K miles so he did a 60K tune-up. The hesitation remained. A few months later the engine check light comes on. My mechanic checked the code and it showed two Ox sensors. I had the Ox sensors replaced and the check engine light went out for a few days. The hesitation remained. It turned out at the same time I needed new rear tires. I went to Tire Pro and the mechanic there checks the engine light code and it returns a mass air flow sensor problem along with two ox sensors. The Tire Pro mechanic indicates that the mass sir flow problem may throw the ox sensors code and a complete diagnostic is needed.

My dilemma is should I go back to my mechanic or take it several miles to the Porsche mechanic for the complete diagnostic. Both my mechanic and the Tire Pro guy indicate that the mass air flow problem is probably causing the hesitation, although the Tire Pro guy mentioned some special equipment needed to fully diagnose the problem. My mechanic indicates that if the sensor is bad he can just change it out - not a problem. This time he'll do that before changing the Ox sensors.

Has anyone had experience with the mass air flow and is a more thorough diagnostic necessary? If this was the problem all along why didn't it show up in the earlier code check?

Thanks in advance for any help with this problem

If the mechanic misinterpreted the codes and you are posting what he said we have much less chance of diagnosing it than if you tell us the codes.

The codes were P0102, P1126 & P1133

The MAF is reporting too low a voltage (P0102) so the car will try to compensate for the lean condition by adding fuel. But it will only throw in so much extra fuel before it throws its hands up in the air and says "I give up. I'm at my enrichment limit" (P1126 & P1133).

It is possible that it is a wiring problem with the MAF but since the MAF is indeed a weak point that is known to fail, I would consider the MAF itself a prime suspect.

The first diagnostic test would be to check (through OBD2 is the easiest way) to see what the MAF is reporting. On failure it has a tendency to have too low a voltage and only lazily go up when the engine is revved. If that is the behavior, you can double-check that the ground wire is not shorted to power (my crystal ball says it's not).

You can try cleaning the MAF, carefully, without touching the film and that might temporarily fix the problem.

Once you've done all of that, get a new MAF (about $230 from AutohausAz.com), plunk it in, reset your mixture parameters by disconnecting the battery, let it run (probably poorly at first) for a few minutes, and you're done.

There may also be a software upgrade that you can apply that will allow you to use a more robust MAF. I can't remember if that applies to your year.

I had a hesitation issue similar to yours, the car would cut out at ~5500 RPM. It felt like I hit the rev limiter. Based on feed back from various boards, replacing the MAF seemed to be the consensus as there was no CEL at the time. I replaced the MAF and the problem went away. I agree Boxsterra that providing the codes is the next step, but cleaning the MAF is a simple, cheap DIY prior to potentially replacing it. The only tool you need is a security torx bit T20 I believe.

My hestitation is more subtle but cleaning the MAF sounds like a good place to start. I found a tech article that the MAF sensor for my year is susceptaible to particulate and that cleaning may be sufficient. Another tech article indicates that the MAF are commonly misdiagnosted. Air leaks in the connecting air ducts and intake manifold can trigger similar symptoms.

Steve,

I had those type of problems for well over a year in my 2001S and after multiple cleanings of the MAF it still was throwing codes. This spring I finally bit the bullet and replaced the MAF. Bingo, not a single problem now in over 10,000 miles,

Neil