MAF or other?
 

For a few months I was getting the P1128 Fuel Trim Mult System too Lean error code. I would reset and it would come back a couple hundred miles later (or so). The car didn't run poorly.

I sprayed the hoses with ether and didn't find any leaks. I bought an off-brand MAF from Ebay. Since installing this I've gotten lots of new errors:

P11370 fuel trim too rich
P1297 pressure drop between turbo and throttle valve
P1557 charge pressure control pos. dev.
P0411 secondary air injection system incorrect flow detected

I've bought a computer cable and have used Vag-com (shareware version only) to monitor readings. With the old MAF idle air flows were 3.2 and 138 g/s at 6000 rpm. The new MAF has 5.5 idle air flows and 174 at 6000 rpm and 195 at 6800 rpm. The new MAF readings seem more reasonable.

It is possible that the ECU is just not "used to" the new MAF and has to work its way back to accepting higher readings? I did disconnect one leg of the battery for a night. I don't know what this did to the tables. I didn't loose my radio channels.

Oh yes the car is:
Audi TT
2001 quattro
225 HP
(AMU engine code)
~40,000 miles

The new maf readings seam correct. You must have another issue. Either a vac leak or bad o2 sensor.

more errors
 

I was concerned that the idle readings were too high on the new MAF.

Can I get anything useful about the O2 sensor from the shareware version of Vag-com?

Today I got this error every time I restarted the car:
P1297 pressure drop between turbo and throttle valve

I'm preparing to do a pressure test by the PVC pipe method. I hope that this tells me something.

Nah, the idel maf readings are good. I think you may have a boost/vac leak as well as a bad 02 sensor. Im not exactly sure... thats a lot of codes.

Are Group 006 Lambda readings useful? How about Group 001 H02S?

What are they?

When I put the old Bosch MAF in I ONLY get this code:
P1128 Fuel Trim Mult System too Lean

Going to finally do the pressure test tonight. I had to let the glue on the PVC dry last night.

H02s
 

I figured out that the HO2S numbers are corrections made for air to fuel based on what is requested by the programming. I don't know if this uses O2 probe readings.

In examining my numbers I found that the new MAF is getting the max -25 at idle! The old MAF would hit +25 at high rpms. Thus my lean and rich errors. Maybe both MAFs are bad.

Well the 4th code is just related to the SAI system

How is your vacuum at idle?

leak check
 

I found no leaks. I did notice that there is a lot of grime (oil, grease, or something) around the PCV valve. Is that normal or could there be a leak under the manifold?

How do I determine my vacuum at idle?

my analysis
 

Further inspection and pressure test have reveled nothing. I ran several logs with each MAF and no MAF. The old MAF has 2-130 g/s from idle to 6000 rpms. Then new one has 6-195 g/s from idle to 6000 rpms. The average injection period readings with NO MAF almost match the old MAF readings, but the new MAF has lower injection periods for the same engine load.

Most importantly (basis for my analysis):
The HO2S control hits the +25 limit with the old MAF at mid to high engine loads. The HO2S control hits the -25 limit with the new MAF at idle only.

Analysis:
2 bad MAFs

The old one reads too low airflow at mid-high engine load. Fuel is based on the low air flow reading, thus low fuel. This results in too lean because air flow is actually higher than indicated. O2 sensor sees too lean and does a +25 on fuel trim causing a P1128 lean engine code.

The new one reads too high at idle. Fuel is increased for this reading. This results in too much fuel. O2 sensor sees this and fuel trim hits -25. This causes error codes like P1137 (too rich) and P1297 (pressure drop).

Sound reasonable? Missing anything? I'm going try another MAF.

reconditioned Bosch
 

I ended up buying a Bosch (reconditioned not new). So far it seems to have solved my problems. About 100 miles and no CELs. Logging with Vag-com showed 2-185 g/s from idle to 6000 rpms. Injection timings were somewhere between the old Bosch and the ebay MAF. The HO2S control numbers have been smaller.

I did notice driving yesterday a whoosh sound twice (DV failure?)