Mine i$ on the MAF *NM*

So, I think I know the answer to this one, but need a little reassurance. I just changed my air filter for the first time. Who knows how long it was in there, because it was filthy. Took it for a drive and it really starts missing/cutting out at about 4000 RPM. it will hold a steady speed, but really protests if I try to accelerate. I think I read on here somewhere that the MAF takes time to reprogram. If that is true, how long, and is there anything I need to do?

Possibly related, but not sure: This morning (before the filter change) I was accelerating hard and the car stalled without warning at 4500. It started right back up, and I couldn't duplicate the problem. In fact, at 4750 RPM I consistently got a little extra power.
All this seems to point to the MAF, but for different reasons. Am I missing something here?

filter is replaced.

If the cutting out was *not* happening before the filter change then something about the filter change is suspect. Some piece of trash (leaf?) managed to fall off the old filter element and is not lodged at the MAF or perhaps has snagged itself on the throttle body butterfly valve.

Oh, wait I see the cutting out was happening before the air filter change. So ixnay that leaf idea. (One still wants to use caution in removing the old air filter to avoid dumping any trash that is on top of the filter into the air box.)

What you can do is using an OBD2 code reader clear the error codes (even though there aren't any) to reset the long term fuel trims back to their defaults, then disconnect the MAF at the engine wiring harness and drive the car and see if the symptom returns.

This can possibly eliminate the MAF.

But if the engine at any time while you're experimenting exhibits any other untoward behavior, starts making noises, shut the engine off and do not restart but get the car to a qualified shop for expert diagnosis.

Sincerely,

MarcW.

I drove the car three times today. The first two felt like the symptoms described on here regarding MAF problems. Rough accelerating, really sputtering above 3000. Tonight I took it out again, same thing for two minutes, then it cleared up. It is running smoother and pulling harder all the way to redline than it ever has. I will keep watching, but I think things might be OK. Since the first incident was prior to the air filter change, I will still keep an eye on the MAF. 50K, and I assume it has never been changed. I can't believe someone would own a car like this and not maintain it better!

Sure, the air filter was dirty, but this may not be because the previous owner skimped on filter services.

I change the air filter on my Boxster regularly and even so when I change it the filter's quite dirty. (Even the Turbo's filter gets dirty, at least the airbox. I've spotted leaves in the air box.)

As I have mentioned before, the engine air intake of the Boxster is located at a particularly dirty location so the filter's going to look pretty bad pretty quickly if one drives the car much at all especially in dirty/dusty conditions.

Who knows what gas is in the thing, how fresh the gas is and so on.

A 2 minute drive is not really that long of a drive. The engine is still quite cold and according to the owners manual until the engine is warm you should keep rpms below 4K.

As for the 50K miles on the MAF, the MAF can fail at any time, but most don't fail at any time. The MAF is not a regularly serviced item and there's no need to replace it periodically. (As I like to point out had I changed my 02 Boxster's MAF every 50K miles I would be on nearly the 5th MAF and yet I've only had one MAF go bad.

Disconnecting the MAF and seeing if the symptoms remain or vanish with the MAF out of the loop is one way that can help you eliminate the MAF, or confirm the MAF is at fault.

Since the car is I believe new to you, you might consider checking the MAF for any contamination. Perhaps the OP had an aftermarket air filter installed that fouled the MAF with oil/dirt? Be sure you handle the MAF with care and it you do clean it clean it with the proper cleaner. And while you're there it might be worth while removing the throttle body and checking its condition. If you spot oil on the throttle body, any oil at the hose connection just after (downstream of) the MAF, this can be the early warning signs of a going bad AOS. The AOS can fail at any time and 50K miles is as good as any. You can clean the TB with the proper aerosol cleaner and then reinstall it. But if you spot any amount of oily dirt on the TB then the AOS is suspect.

Might want to check the condition of the oil filler tube cap (they can develop a vacuum leak over time) and the coolant cap. This can leak and over time let the coolant level drop to the point the low coolant level warning light will come on. A better cap ends with the part number 02 or 03 or even 04.

Sincerely,

MarcW.

'01 S.
Marc, I have had it for about four months, and am familiar with the way it should drive/sound. This was a sudden change, and when it stalled, it was the first indication of a problem. My comment about the filter being dirty should have said that it looked so old that the foam portion was deteriorating.
what I said about the same thing for two minutes was that about 3000, if I tried to accelerate, the engine would miss and the car would jerk pretty violently. I never drive hard untl the engine is warm. The way this cleared up makes me think the ECU was adjusting. Anyway, I will continue to watch it. Thanks for the help.
Laz, As far as your comment, some of the idiosynchrasies occured right at the point where I would normally expect the resonance flap to kick in. I don't know how to check that, or if that is a part that would benefit from cleaning. Anyway, still learning.

Quote
IFlyLow
'01 S.
Marc, I have had it for about four months, and am familiar with the way it should drive/sound. This was a sudden change, and when it stalled, it was the first indication of a problem. My comment about the filter being dirty should have said that it looked so old that the foam portion was deteriorating.
what I said about the same thing for two minutes was that about 3000, if I tried to accelerate, the engine would miss and the car would jerk pretty violently. I never drive hard untl the engine is warm. The way this cleared up makes me think the ECU was adjusting. Anyway, I will continue to watch it. Thanks for the help.
Laz, As far as your comment, some of the idiosynchrasies occured right at the point where I would normally expect the resonance flap to kick in. I don't know how to check that, or if that is a part that would benefit from cleaning. Anyway, still learning.

behavior at 3K rpms is not a sign of resonance flap problems. I would welcome any correction but I can't remember coming across anyone actually id'ing a problem with resonance flap system in an engine that has been unmolested.

If the car has sat around unused a while the gas could be the problem. It goes stale and stratifies -- this is especially a problem with gas with ethanol in it -- and more than one reported problem that started out similar to yours ended up being 'bad gas'. A bottle or two of Techron used according to directions on the bottle might be of some value.

You have some suggestions as to what to do to try to isolate the problem. Continuing to drive the car is ok, up to a point. However, if the engine starts acting worse, starts making any noises, etc., shut the engine off and don't restart it. I don't think what the engine is doing are signs of a more serious problem -- most of these turn out to be due to a bad MAF, bad gas, bad coils, an air leak, bad AOS, etc., and not pending engine failure -- but be aware there can be exceptions.

Sincerely,

MarcW.

Thanks,
I have a Durametric, and will check it out. Undoubtedly more to follw. BTW, thanks for all the responses. I learn something new every time I log in.

what year is this car?

These cars have lots and lots of sensors in them. The problem you are describing could be MAF, could be O2 sensors, could be a bad throttle position sensor, or could be a bad coil. My O2 sensors went bad and created similar symptoms to what you are describing. My MAF also went bad and created similar symptoms to what you are describing. A bad coil will also create similar symptoms to what you are describing.

Marc's first suggestion is a good one - get a Durametric ($40 at an autoparts store) and read the codes. Even if the CEL light is not on, you WILL have codes because the symptoms you are describing are not normal and the ECU will throw codes. Based on those codes, we can probably diagnose the problem.

1998 986 Turbo-Look Cab
172,000 Miles
Dilithium Crystal Supercharger

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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I believe in doing the cheap things first, if this is an early car it has a fuel filter. If the air filter was that bad then the fuel filter is due . It may be not cure the problem but it does sound like a fuel delivery problem . You would think you would be getting a fault code.