Audi A6 TDI 2007 Runs Rough

[Tonychestnut]

Hi All

this is a similar issue to one other I have seen here however with subtle differences as follows.

A6 2.0l 6 speed.
Issue
Car hesitates/jerks and runs rough anywhere from 1200 rpm to 2200 rpm.

When accelerating from stopped, when the car reaches approx 1800 rpm in 1st, the car suddenly hesitates or jerks. Same thing happens in second and so on up through the gears but less noticeably in higher fears. When cruising, it manifests as a roughness in the engine. It can be so bad that you can see it on the rpm gauge. When it starts to happen in 1st, if you hold the throttle steady at the same rpm, the engine hunts ie, speeds up and suddenly dies etc etc. It is also producing a lot of black smoke on acceleration and is generally down on power.

It has gotten to the stage when it is continually happening when cruising on the motorway at around 2000 rpm which is rendering the car practically undriveable..

The following has been done.
Fuel filter changed and fuel tested for oil (non present)
EGR Valve replaced
Mass Airflow Sensor Replaced
Intake manifold removed and cleaned.
Turbo intake hose checked for leaks (none
ECU Upgraded to newest version of software available (by Audi)
Total spend over €1000

All to no avail.

Two interesting points however,
When I disconnect the Mass Airflow Sensor, the car runs perfectly smoothly all the time (if very slightly down on power). I understand that disconnecting the MAF tells the ECU to leave the EGR Valve closed.
In addition, on first start when the engine is stone cold, the issue never happens when I go up through the gears for the first time but after a minute or so, it starts to happen and then continues.

Any help anyone, I am pulling my hair out and am beginning to think that the only way to fix the problem is to buy a box of matches !!

 

[desertstorm]

I would say you have a boost leak somewhere. Check ALL the boost hoses for wet patches of oil. And the intercooler to make sure there are no splits . The MAF is recording air entry into the engine and provides fuelling to match. However with the boost leak there is actually a lot less air getting into the engine hence the black smoke.
Disconnecting the MAF the ECU switches to another strategy where it calculates the approximate amount of air entering the engine based on boost and RPM.
With the boost leak the VNT on the turbo will be held closed in an attempt to try and spool the turbo and this causes quite a restriction in the exhaust.

 

[Tonychestnut]

I would say you have a boost leak somewhere. Check ALL the boost hoses for wet patches of oil. And the intercooler to make sure there are no splits . The MAF is recording air entry into the engine and provides fuelling to match. However with the boost leak there is actually a lot less air getting into the engine hence the black smoke.
Disconnecting the MAF the ECU switches to another strategy where it calculates the approximate amount of air entering the engine based on boost and RPM.
With the boost leak the VNT on the turbo will be held closed in an attempt to try and spool the turbo and this causes quite a restriction in the exhaust.

Thanks desert storm. I have already checked the compressor inlet hose which is OK but have yet to check output through the intercooler etc. Forget to say also that there are no fault codes whatsoever except when I disconnected the MAF sensor when I got the code for the sensor and also Turbo underboost which I would assume is also as a result of disconnecting the MAF.

 

[desertstorm]

You a re more likely to get an underboost code with a boost leak. You may have to get the front bumper off to check all the hoses and intercooler.