ONAFLYER

My Durametric tells me this is MAF, below lower limit.
It tests fine with .99volts key on, 1.3-1.5 at idle.

My car has the larger air box from a 987 in it, and a new Bosch MAF, cat-less mid pipes and a rebuilt engine. 2002 986 S.

Can the DME "learn" with a fault code looming? I have just over 500 miles on new engine.

Thanks

Macster

The DME can learn, in fact it has, and it has learned something's not right.

What are the long term fuel trims?

The presence of a non-factory air box can affect air flow through the MAF. The MAF is designed to somewhat insensitive to this but there's a limit to how insensitive it can be.

Next, I'm on less firmer ground but I seem to recall a few posting issues with non-Porsche MAFs.

Also, you can't eliminate a bad MAF. Even a new one can be bad, or go bad shortly after it is put into service.

You might just proceed with the assumption the MAF is bad. I'm not suggesting you trash the current MAF and replace it only that you try to get ahold of a factory MAF intended for your car (for the part number my parts manager contacts tell me use the car's VIN to determine which MAF is suitable) and then see if the symptoms/error codes return.

Before you do this be sure the MAF is securely connected to the car's wiring and the MAF is properly installed.

Sincerely,

Macster.

ONAFLYER

When I attempted to have the car smogged last month, it was rejected for:
OBD Evap inop, and OBD Second air inop. No check engine at the time..

So does a MAF code keep those systems from operating properly?

The air pump comes on at cold start every time and runs for about a minute, and I can manually turn on the pump with Durametric.

Byprodriver

Not long after I rebuilt my 2000S engine to a 3.6 I was getting SAI & EVAP codes (don't remember the numbers) & P1128 & 1130 also rough idle. Replaced MAF sensor & it fixed everything. Have you tried disconnecting MAF & driving?

ONAFLYER

I did that originally, which led me to believe it was bad. Thats why I bought a new Bosch unit. At first it was better, maybe it is bad too. Even though it reads the correct voltage. I've been selling parts for a while now, and I know sh*t happens all the time.

Thanks

Macster

I vaguely recall at least in some cases all other systems have to be ok before a specific system can be tested by the DME.

Thus (IIRC...) a bad MAF or one that is on its way to being flagged bad may effect other emissions related systems. Since the evaporative system can dump fuel vapor into the intake the DME has to have pretty high confidence other systems are operating ok cause this extra fuel could overheat the converters and these are expensive and covered by Porsche under the extended emissions warranty. So of course Porsche is going to be very careful with those babies.

If the two readiness monitors associated with the evap and secondary air systems were not set to complete, they were flagged incomplete and two incomplete could be sufficient reason to fail the car. (In CA I think we're allowed up to 2 readiness monitors set to incomplete. NV may be different.)

Also, the evap system non-operational and secondary air non-operational may have been pending codes, which could be reason enough to fail the car.

You are faced with a process of elimination and while this is not a recommendation to replace the MAF you might want to try running with the MAF disconnected. Be sure you clear any codes to among other things reset all fuel trims to their defaults.

However, with the MAF disconnected this may simply be at some level interpreted by the DME as a bad MAF and you get the same results.

It looks like you caught between a rock and hard place, but let me think about this some more...

Sincerely,

Macster.

ONAFLYER

Thanks for your input.

So last night I re-installed my "new" Bosch MAF sensor, and added a restriction to the inside of the larger air tube, reducing it's inside diameter. Cleared codes.

Then I went for a drive, after noticing a much smoother idle. No check engine light, smooth idle still, it's done this before, and running reasonably well.

Driven it two more times including to work in sub-20 degrees this morning.

So far no light...........need to check the systems now.

Macster

You might be on the right track. How many miles did you drive? My experience that in order to verify/confirm a problem that was generating a CEL has in fact been fixed is that a 30+ mile drive is required.

This involves starting the engine from cold, giving the engine some idle time (typically I let the engine idle until the secondary air injection pump shuts off), then I just drive the car normally. City (stop/go), low to medium speed steady state cruising, and some high(er) (highway) speed crusing. This is about my work commute.

Sincerely,

MarcW.

ONAFLYER

After another short drive of less than 15 miles, still no cel light. And I plugged in the computer to check for status, shows all pass except for Sec Air, on a warm car. Which is enough to pass smog here. We are allowed only one fail.

I plan to replicate the entire EPA drive cycle next, which I believe is over 30 miles as you said.

Any thoughts on covering the filter instead of reducing the tube diameter? I might even block a portion of the tube at origin from the housing, which would allow "tuning". I may have restricted too much for now, I just need to get it smogged first.

Thanks,
Drew

Macster

In some cars there's a screen (of some kind) in the intake between the airbox/filter and the MAF (usually just ahead of the MAF). This screen is there if my memory isn't failing me to smooth out in some way the air flow so the MAF works better.

It has been years ago -- back in early 2004 -- since I last had my hands deep inside my 02 Boxster's intake system (the intake system from the filter box to the TB) and I can't recall any screen being there but you need to know and if there's one in the stock air intake system, the modified air intake system should have one too, something similar.

If I'm not totally clueless, this could be the solution to the CEL and you do not have to jury rig something to make the MAF behave.

Sincerely,

Macster.

ONAFLYER

The stock air box does not have a screen IIRC, but the 987 MAF has a separate housing with a screen on the leading edge. This could be the spot to work with, yes. It is not the easiest to get to, but I could do it. Every time it gets quicker to take in and out.

I think I need to stay in close proximity to the sensor, too far away may not accomplish the same effect. At first the car would not accept full throttle, and now I can get to 5k before it stumbles. Its learning again it seems.

Thanks,
Drew

ONAFLYER

I passed smog, all systems working. Nice to be done with this.