audi tt, 1.8 T, 225 HP - rpm variations at deceleration and other problems

Hi everybody,

Please take a little time for my rather long story, but consider the fact that I' am struggling with this matter for more than a year.
I've bought a Audi TT 1.8 Turbo, quattro, 225 HP with APX engine, from the year 2000 and soon I have discovered that the turbine (turbocharger) is broken - was throwing oil in the exhaust system and the effect was a black smoke.
I've changed the turbine, then because VAG-COM reported a error I've changed the Lambda oxygen sensor everything was OK in respect with the VAG-COM, or at least I got no more errors.

Then I have noticed ( I don't remember if this happend before I changed the turbine) this strange behaviour: whenever I relase too suddenly the throttle pedal I hear a noise in the air filter area (some kind of rattling) and the engine rpm drop dangerously to a 400 - 600 rpm. Sometimes in slow speed corners the engine stops.

For this I have changed the throttle body with a new one, after many calibrations and cleanings - no difference.

Recently I have changed the debitmeter with a new one and everything got crazy. First the car worked almost as before - with a small lack of power when I begun to press the acceleration pedal.
When I stoped after few kilometers I received the error:


Control Module Part Number:
Component and/or Version: 1.8L R4/5VT 0001
Software Coding: 05710
Work Shop Code: WSC 00000
1 Fault Found:
16486 - Mass Air Flow Sensor (G70): Signal too Low
P0102 - 35-00 - - - Intermittent

Then I cleared this error, made another few kilometers and I got:


Control Module Part Number:
Component and/or Version: 1.8L R4/5VT 0001
Software Coding: 05710
Work Shop Code: WSC 00000
1 Fault Found:
16514 - Oxygen (Lambda) Sensor B1 S1: Malfunction in Circuit
P0130 - 35-10 - - - Intermittent

I cleared also this error, I have callibrated the throttle body and I got again the Lambda error.
I have cleared again the Lambda error and then the car became not stable when I started it. It didn't start at the first few tries, I got a huge rpm variation, I got explosions in the exhaust etc...

I had to disconnect the debitmeter (pulled of the power cable) and the car worked different in the sense that it was the first time I didn't experienced rpm drops, although the noise in the air filter area was still persistent. But, I couldn't go over 3500 rpm - it was clear that this was not the fix.

In the next morning I have connected the debitmeter back, got difficulties when I tried to start the engine but I have hepled the engine to start by pressing hard the throttle pedal. Whenever the engine passes the first phase, with the acceleration help it goes to a "normal" behaviour.

Because I got again the Lambda error I have put it out and clean it, although it was allready clean. From then on I received no more Lambda errors.

I have drove the car, with a difficult start, but then it worked fine, on the highway with 130 - 160 km/h. When I got off the highway, after couple of kilometers with 40 - 100 km/h, the ESP warning on bord lighted up. I have stoped and I have seen that I had the new error:

Control Module Part Number:
Component and/or Version: 1.8L R4/5VT 0001
Software Coding: 05710
Work Shop Code: WSC 00000
1 Fault Found:
16487 - Mass Air
Flow Sensor (G70): Signal too High
P0103 - 35-10 - - - Intermittent

Even though I have cleared the error in the next 100 km it appeard again a couple of times everytime announced by the ESP on bord.

I stoped, cleared the error, didn't start the car for few days then I made around 300 KM - normal rode and highway. I had dificulties to start the car but then it worked almost like before I changed the debitmeter and ... I got no more errors! The next day, after a difficult start I drove around 10 km but again no errors.

What I have noticed and I believe it is important is that whenever I have dificulties to start the car, in the "001" Measuring Blocks field in VAG-COM I got at "HOS2 Control" a constant "25%" value. Anytime else I got a constant variation from -7% to +10%.

Well, that's the story... If it not clear please indicate me what else should I do and what other data may I offer you. Maybe based on your experience you can help me clarify:

- why the car is producing a rattling noise while decelerating in the air filter area? I believe that it is relared with the "cut-off" valve but how can I decide it is broken, what experiments should I make, what data in VAG-COM should I follow?

- why is the rpm dropping when I take the foot off the pedal?

- is the new debitmeter broken, or is the old one but in such manner that it hides some of the car's vices?

- what do you think I should do to solve the problem or make it clear?

- should I post this also on General Tech area for better chances for anwers?