audi tt, 1.8 T, 225 HP - rpm variatins 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, 225 HP from 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 droping 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?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com wrote:

US but a Google seems to indicate that it is the Diverter Valve that you are referring to. The DV may be at fault causing boost problems but probably not the cause of most of your issues.
A rattle under deceleration is often associated with a failed Waste Gate actuator which is part of the turbo but can be replaced separetly for about $180 US parts cost. If this is the problem you would experience loss of boost under acceleration but it would not be the reason that you are getting codes.
I would guess that you had a loose connection of the O2 sensor. Crimped wire connection are preferred over soldered when replacing with generic.
I don't remember you saying that you replaced the MAF. If not that is the first thing I would suggest and then see what codes you get. The MAF can be cleaned but replacing it is a more certain fix.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

All appologies! By debitmeter I was reffering to MAF! I have placed back the old MAF and the errors dissapeard. The turations still drop though... and the sound is still scratching my nerves. So you are saying that is the "Waste Gate Actuator"... Is this the term audi uses as well for this part? Well I will look for this part, see where is located but meanwhile I have ordered a Diverter Valve because someone told me that the sound can be associated with DV. What do you think about that?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com wrote:

"Waste Gate Actuator" is the term that is used in the US and I would guess most other English speaking countries. It is an assembly that is attached to the side of the turbo and is usually considered a part of the turbo but can be changed separetly. Replacing it requires remocing the turbo. I was just guessing that this might be your problem. Be sure to diagnose the problem before spending money and time on it.
A failed waste gate actuator can be diagnosed visually. With the engine off, look down the exhaust side of the engine and see the turbo. Between the turbo and the engine you will just barely be able tyo see a shiny steel rod running forward and back. That it the actuator rod. Use a stick to reach down to push on the shiney rod Try to move it back and forth. If it moves at all it is bad otherwise it is probably fine.
Changing the DV is a good idea and may help. It would have been a good idea to pressure test the system for leaks and observe boost with a gage to see if you have a problem with it before buying parts.
Let us know your progress.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hello,
Well I have finally replace the DV. The resoults are good: the noise dissapeared or at least is hardly noticeable and the rpm drops are now smaller and rarely appear. But... to be able to use the car untill I got the DV I have put back the old MAF and I have returned the new one (I descriebed the problems related with the new MAF in my first post). Since then I experience a engine power loss. I am still hearing the turbo but the car lacks power. Please see the VAG-COM log file in which I have also generated a graph: http://www.yousendit.com/download/WFJVblFBYTIrV3cwTVE9PQ What I suppose is that there is a problem with the turbo pressure because the actual pressure (@Intercooler) (with the red color), is allways less than requested presure - yellow. In fact the pressure only incerases if I press at once and very hard the gas pedeal. If I press it gredualy nothing happens. Is this normal? With blue are the rpm. With green are the verry slow values recorded by the MAF. What do you think about these measurements?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com wrote:

combined with a vacuum leak.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

location: Washttp://en.wikipedia.org/wiki/Wastegate and I have seen the last paragraph - "Wastegate chatter myth" which seems to completly explain the noise I experience. Long story short, it says that the turbine makes the noise but the cause is DV not WGA.
Anyway, I will check the turbo system, including WGA.
If you have any other ideea please tell me. Is possible to experience the above issues because of the pressure sensors?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com wrote:

and it rattled. I could also rattle the rod with a stick. We pulled the K03 out and verified that the WGA was bad because it had no resistance. We replaced the WGA from a spare K03 and the problem was solved and boost was back :-)
Your issue may well be different.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.