1128 & 1130

[TerryT]

Hi,

So I did the following :

1. Confirmed I have a clean air filter.
2. Cleaned the MAF with a MAF cleaner from Advance auto parts.
3. Cleared the codes.

And then :

Car seemed to be fine, no problem... but then again there was no problem before really. CEL light came on again at about 100 miles.

So should I get a new MAF or could it be something else entirely ?

Or should I just take it to dealer and hope the warranty covers it ?

Thanks
Terry

[paulv]

Terry,

Here's the info for P1128 & 1130:

Fault condition:
Fuel/air mixture so lean that sensing has reached its rich threshold.

Potential fault areas:
– Incorrect signal from MAF sensor
-- MAF is failing
– Intake air system leaking
-- Air is introduced past the MAF causing the mixture to be more lean
– Fuel pressure too low
-- Not enough fuel to meet demand causing the mixture to be more lean
– Volume supply of fuel pump too low
-- Not enough fuel to meet demand causing the mixture to be more lean
– Fuel injectors fouled
-- Not enough fuel to meet demand causing the mixture to be more lean
– Exhaust system leaking
-- When the exhaust system has leaks before the front O2 sensor will cause the O2 sensor to report a lean condition (excess oxygen i the exhaust)

BTW, I agree with Meir's recommendation. I have the Durametric tool and could have ruled out the MAF sensor in a couple of minutes (with the service info) -- with the key on and engine off, the MAF voltage should be approx 0.9 to 1.1 volts -- at idle, the voltage should be approx 1.4 volts.

Regards,
paul...

[TerryT]

Originally Posted by paulv

Terry,

Here's the info for P1128 & 1130:

Fault condition:
Fuel/air mixture so lean that sensing has reached its rich threshold.

Potential fault areas:
– Incorrect signal from MAF sensor
-- MAF is failing
– Intake air system leaking
-- Air is introduced past the MAF causing the mixture to be more lean
– Fuel pressure too low
-- Not enough fuel to meet demand causing the mixture to be more lean
– Volume supply of fuel pump too low
-- Not enough fuel to meet demand causing the mixture to be more lean
– Fuel injectors fouled
-- Not enough fuel to meet demand causing the mixture to be more lean
– Exhaust system leaking
-- When the exhaust system has leaks before the front O2 sensor will cause the O2 sensor to report a lean condition (excess oxygen i the exhaust)

BTW, I agree with Meir's recommendation. I have the Durametric tool and could have ruled out the MAF sensor in a couple of minutes (with the service info) -- with the key on and engine off, the MAF voltage should be approx 0.9 to 1.1 volts -- at idle, the voltage should be approx 1.4 volts.

Regards,
paul...

Excellent post Paul, thank you!

I will be getting the Durametric tool, but possibly only within the next few weeks.

My CEL comes on with these codes when I am idling, not when driving... would that narrow the list down somewhat ? Any ideas why it would happen then ?

Thanks again.
Terry

[paulv]

Originally Posted by TerryT

Excellent post Paul, thank you!

I will be getting the Durametric tool, but possibly only within the next few weeks.

My CEL comes on with these codes when I am idling, not when driving... would that narrow the list down somewhat ? Any ideas why it would happen then ?

Thanks again.
Terry

Terry,

You're welcome!

My first guess would be to check for leaks in the air intake system which would allow air to enter at idle when the intake vacuum is very high. When driving, the intake vacuum is very low because you're [normally] drawing in air into the intake so very little air can be drawn in from the outside of the intake. A good way to see this is with a full OBD2 scan tool (which has Mode $07) to monitor the Long Term Fuel Trim (LTFT aka Fuel Adaptation) for each bank where you would see the LTFT reading going positive high (more rich) at idle and then coming back to normal at approx 2000 rpms.

Since you're getting this code for both banks, then the problem is not bank-specific (at least it appears that way).

My second guess would be to check the exhaust for leaks, but then again, both bank codes are appearing which leads me to stay with my first guess.

Intake vacuum leaks are a hassle to look for unless you have a smoke machine (which most of us DIY'ers don't own due to costs), but you can still look. While the vehicle is idling, check all the intake plenum parts, the AOS*, and all other lines going into the intake for signs of leaks (noise, cracked hoses, etc). There are a couple of other methods but I don't recommend them because if misused, they can cause serious problems.

Since the car drives OK, then the fuel delivery system is probably OK.

Good luck.

Regards,
paul...

*AOS = Air Oil Separator, which is a sophisticated version of a Positive Crankcase Ventilation (PCV) system. Besides the PCV function, the AOS helps to prevent foaming of the oil. Also, check out Pelican Parts as Wayne has published some great and inexpensive books on Porsche repairs and also has many tech articles that can help you.

[fullthrottle52]

Get a new MAF Sensor. Cleaning does not always work. Also check for air leaks. A good mechanic will smoke test the engine and look for leaks. I had the same problem and found a slit in the oil filler tube. Replaced the filler tube and still had CEL. Replaced the MAF and gone for good.