A4 TFSI Quattro Engine trouble...

Hi guy's I am looking for some advice regarding the B7 2.0 TFSI motor.
I purchased the car recently and it had very rough idle and used to rev up to ~2000 RPM at junctions and try and shake itself to bits at around ~500 RPM so I replaced the PCV valve and improved it a great deal.

Prior to replacing the PCV valve I had a fault code stored on the ECU - P0171 Bank 1 too lean, I cleared this and it went away after replacing the valve for a couple of hours then came back, the rough idle was much better.
The engine still feels slightly under-powered and I have noticed that once the engine is up to temp the idle sits around 1100-1200 RPM which is not right so I can assume that I have a hose split or faulty sensor maybe?
Another thing to note is that when engine braking in 3rd or 2nd gear it feels like it is still pulling rather than slowing, maybe that is just me coming from a Skoda Octavia VRS Diesel to a petrol unit I don't know but it does not seem correct.

I have had the car in to be looked at today and the technician had checked for a vacuum leak and plugged in the VAG-COM diagnostics, sure enough the P0171 code is still present, however he could not give me a diagnosis.
What the guy suggested was to pull off all of the hoses and inspect them, however I aint got a clue where to start - any ideas?

Cheers

Rob.

Ok, after spending loads of money on finding the route cause of fault code P0171, rough idle, revs holding high whilst engine braking and lumpy performance I think I might have found the problem.
After checking the MAF, replacing the PCV, checking for vacuum and air leaks and spending fortunes on diagnostics I managed to get a schematic drawing of the TFSI engine from some hooky website dishing up VAG internal documentation, so lets walk through this from day 1 addressing each step taken:

1. Bought the car from dealer in Scotland, got the car home and noticed really bad idle and revving at junctions, scanned ECU and found P0171 Bank 1 too lean.

2. Searched forums for identification of symptoms, advised to do the PCV test by pulling the dip stick or the oil cap off whilst the engine was running, failed that test so replaced the PCV which resolved the rough idle and revving whilst in neutral.

3. The fault code P0171 persisted and paid several "VAG specialists" to diagnose the fault, no joy they came to the same conclusion that they could not find any fault.

4. Took the car to Revolution in Dunston and asked them to look at the problem, another dead end.
Promised to call me back the following day and discuss the test results from VAGCOM with possible solutions, never got the call - after waiting two hours over my initial booked appointment for them to pi$$ me about and not have the decency to contact me as arranged, safe to say they will not have any repeat business.

5. Had the car serviced at Swift Motor Engineering in Westerhope and they had the engine smoke tested, was told the possible cause of the P0171 fault was due to the PCV valve I purchased from GSF Car Parts as it was not a OEM part, this is not the case.

6. After speaking to BFT John he advised me to check the MAF Sensor by replacement, thanks for the help John, firstly I removed the entire MAF assembly and cleaned the actual MAF Sensor unit which I removed from the tubular housing - the MAF was brand new and cleaning made no difference so called in to Vee Dubb's down Bill Quay in Gateshead and swapped my MAF for another unit, results exactly the same so the MAF was ruled out as being faulty.

7. The guy at Vee Dubb's removed and inspected the Turbo Diverter Valve solenoid unit and we concluded that was ok, it was new and the improved version over the old problematic unit so that was ruled out as the source of the air leak.

8. I took the car home and removed the throttle body and checked the motor gear and electronics, all seemed fine with that, cleaned the small amount of crud from the butterfly anyway as I went to the trouble of removing it.

9. So, after having the car scanned several times with VAGCOM (cost me each time!) and using my own ODBII Software (Torque) which very good for the few quid I paid for it, I performed several road tests, each time performing data-logging on each journey then loading these test results in to an excel pivot table so I could graph the what the engine was doing over the course of 20 test drives using mixed driving styles.
The results of these tests are that each element of the engine was performing correctly and within tolerance, turbo boosting fine, MAF reading fine, BHP at wheels - as expected, 02 Lambda within limits etc etc.
So, where next?

10.
Booked the car in to my old faithful no-frills mechanic and had the car all day at a cost of £10, I gave him £20 for his trouble, this yielded no results other than the throttle body being a possible suspect.

11. Ok, so now I am at a dead end, what could be the problem, I am a software engineer not a mechanic so my skills are limited - or are they, I took a step back and started reading the engine diagrams that I obtained and started looking at every possible way that un-metered air could enter the TFSI Motor, I worked from the Air Intake and went right out the entire system, including the rocker cover and PCV system and ended up at the final system that interacts with the air/fuel combination of the engine - the EVAP re-circulation.
I studied this system from VAG documentation and internet chatter and as most of you may know, the EVAP system receives Petrol fumes from the fuel tank, passed through a charcoal canister, mixed with air and fed in to the intake manifold via the N80 valve.
Now, what would happen if this valve was faulty? Well depends on how it fails, in my case I have drawn the conclusion that the valve was stuck open and the air/fuel vapour was mostly air due to the valve being stuck open, thus un-metered air getting in to the intake manifold causing the problems I have been experiencing.

Hope this helps and saves you a few quid and months of headaches.

Cheers

Rob.

Mike.M said:

What miles has yours done?

Wifes Golf with similar engine hit 80k miles and started to play up.

Have you done a compression test. Had this on the wifes Golf and we had to take the head off to de-coke all the valves, a very light skim for peace of mind and rebuilt again with new chain, guides etc as it had stretched about 15mm and also contributed to an additional misfire..... Unfortunatley we also had to change the faulty NoX sensor which was expensive at £350 trade prices...........otherwise after about £2.5k spent all is fine and like new again, and mostly caused by the EGR.

Click to expand...

Hi Mike,
the car has done 160K backed with full Audi service history.
I intent getting the head removed and have the valves de-coked as its direct injection the valves will never benefit from treatment such as Redex or STP Cleaners.

Cheers

Rob.

Spoke to my mechanic today and we discussed having the engine de-coked, he said going to all the trouble of having the head removed may aswell replace the valves as they are not expensive.
So, best start putting the pennies in the jar and get saving, at least I will have confidence in the car after all this money has been spent, won't add anything to its value however I plan on keeping it for at least another 100K Miles, its become a labour of love more than anything, I could have stayed with my old faithful Ford Mondeo's but nothing comes to close to owning a 200BHP Quattro, power and traction coupled with style too.