P1128, P1130 Solved

[ar38070]

So I finally fixed this problem and it did turn out to be the MAF. This is a 1998 Boxster with 61K miles. The OBDII readout of the Long Term Fuel Trims were 29.7% For those who have this problem in the future this is what I tried:

Changed the plugs

Changed the fuel filter

Used a bottle of techron

Searched for intake leaks

Checked the oil separator bellows

Checked the oil filler tube

After all this I did notice a slight improvement in the fuel trim numbers. They decreased to about 27% but I would still eventually get a CEL.

One other symptom was that the car would stall once when cold.

I then conned Trygve into letting me use his car as a guinea pig. I took MAF readings from his car at various RPM and got:

idle 3.6 g/s

2000 rpm 7.8 g/s

2500 rpm 11.4 g/s

3000 rpm 14.8 g/s

3500 rpm 16.2 g/s

4000 rpm 17.8 g/s

4500 rpm 22.3 g/s

On my car the numbers were:

idle 3.5 g/s

2000 rpm 7.2 g/s

2500 rpm 10.0 g/s

3000 rpm 11.7 g/s

3500 rpm 12.8 g/s

4000 rpm 15.0 g/s

4500 rpm 17.9 g/s

So my numbers were some 20-30% low. We then swapped MAFs and the problem followed the MAF. So I bought a new MAF, installed it and now my car reads:

idle 4.4 g/s

2000 rpm 8.0 g/s

2500 rpm 10.3 g/s

3000 rpm 14.0 g/s

3500 rpm 16.2 g/s

4000 rpm 19.4 g/s

4500 rpm 23.2 g/s

It was about 75 degrees during the first two readings and 65 degrees for the last set.

As posted previously the best source for the MAF appears to be:

http://www.autohausaz.com/catalog/lookup_p...FToken=80622876

The part I got even had the Porsche Part number (996 606 123 00) on it.

You can get a set of security or tamperproof bits (you need a Torx T20 security bit) here:

http://www.harborfreight.com

Item number 91310 for $7.

I would suggest that if you have an OBDII reader that you take baseline readings of your car so that if you have a problem in the future you know what your readings are for when the car was running properly.

[GaryFB]

Excellent procedure and invaluable data. Thank you - Gary

So I finally fixed this problem and it did turn out to be the MAF.  This is a 1998 Boxster with 61K miles.  The OBDII readout of the Long Term Fuel Trims were 29.7% For those who have this problem in the future this is what I tried:

Changed the plugs

Changed the fuel filter

Used a bottle of techron

Searched for intake leaks

Checked the oil separator bellows

Checked the oil filler tube

After all this I did notice a slight improvement in the fuel trim numbers.  They decreased to about 27% but I would still eventually get a CEL. 

One other symptom was that the car would stall once when cold.

I then conned Trygve into letting me use his car as a guinea pig.  I took MAF readings from his car at various RPM and got:

idle 3.6 g/s

2000 rpm 7.8 g/s

2500 rpm 11.4 g/s

3000 rpm 14.8 g/s

3500 rpm 16.2 g/s

4000 rpm 17.8 g/s

4500 rpm 22.3 g/s

On my car the numbers were:

idle 3.5 g/s

2000 rpm 7.2 g/s

2500 rpm 10.0 g/s

3000 rpm 11.7 g/s

3500 rpm 12.8 g/s

4000 rpm 15.0 g/s

4500 rpm 17.9 g/s

So my numbers were some 20-30% low.  We then swapped MAFs and the problem followed the MAF.  So I bought a new MAF, installed it and now my car reads:

idle 4.4 g/s

2000 rpm 8.0 g/s

2500 rpm 10.3 g/s

3000 rpm 14.0 g/s

3500 rpm 16.2 g/s

4000 rpm 19.4 g/s

4500 rpm 23.2 g/s

It was about 75 degrees during the first two readings and 65 degrees for the last set.

As posted previously the best source for the MAF appears to be:

http://www.autohausaz.com/catalog/lookup_p...FToken=80622876

The part I got even had the Porsche Part number (996 606 123 00) on it.

You can get a set of security or tamperproof bits (you need a Torx T20 security bit) here:

http://www.harborfreight.com

Item number 91310 for $7.

I would suggest that if you have an OBDII reader that you take baseline readings of your car so that if you have a problem in the future you know what your readings are for when the car was running properly.

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