2004 Touran 1.9 TDI Flat spot when warm

[gkm24]

I have a 2004 Touran 1.9 TDI which starts and runs perfectly.
From cold, when pulling away, there is loads of torque and it pulls away as it should. When it gets up to temperature there is no torque when pulling away and you have to get the revs up to get going as if the variable nozzles are open and not spooling up the turbo.
I have checked the vacuum unit and it works perfectly and holds a vacuum. The lever that operates the vanes works smoothly. The vacuum line from the controller is fine and holds a vacuum.

One other thing is that when trying to pull away through the "Flat spot" there is some black smoke as if the engine is getting the fuel but not the boost.

Does this sound like turbo?

Thanks for any help.

[gkm24]

I have a 2004 Touran 1.9 TDI which starts and runs perfectly.
From cold, when pulling away, there is loads of torque and it pulls away as it should. When it gets up to temperature there is no torque when pulling away and you have to get the revs up to get going as if the variable nozzles are open and not spooling up the turbo.
I have checked the vacuum unit and it works perfectly and holds a vacuum. The lever that operates the vanes works smoothly. The vacuum line from the controller is fine and holds a vacuum.

One other thing is that when trying to pull away through the "Flat spot" there is some black smoke as if the engine is getting the fuel but not the boost.

Does this sound like turbo?

Thanks for any help.

Today I plugged in the vcds to see what was going on and there were no codes at all. It seems to be getting worse as it warms up but still on initial start up from cold it pulls like a train. Its getting a bit dangerous to pull out onto a busy road now as it absolutely has no go whatsoever and then the next time you pull up it pulls away like a train again.
Im leaning towards MAP sensor. Can anyone concur?

Thanks for any help.

[Roverfan]

Today I plugged in the vcds to see what was going on and there were no codes at all. It seems to be getting worse as it warms up but still on initial start up from cold it pulls like a train. Its getting a bit dangerous to pull out onto a busy road now as it absolutely has no go whatsoever and then the next time you pull up it pulls away like a train again.
Im leaning towards MAP sensor. Can anyone concur?

Thanks for any help.

I would watch the live data when it is occurring. If it only happens when warm perhaps warm the map sensor with a hair dryer to see if it effects the sensor circuitry when the vehicle is cold - is another way for an accurate diagnosis

[Roverfan]

I would also see if it runs better with it unplugged, or the MAF unplugged.

[gkm24]

So I took it out for a run this morning and it ran great until it got warm and then was terrible when pulling away. I pulled over and unplugged the MAP sensor and that made it even worse so I pulled over again and reconnected it but unplugged the MAF sensor. Pulled away with loads of power and goes really well now, so have ordered a MAF sensor. I would have thought that unplugging either of these sensors would have thrown up the engine light but it didn't.

[Crasher]

So now you have MAP, IAT, and Mass Air Flow sensor errors to lie on top of what was there before without having a clue what was there before... not the right way to do things....

[gkm24]

I knew you would tell me off and you will tell me off again. You are right as usual that its not the right way to do it.
So I got a replacement MAF and fitted it but it is exactly the same as before. It pulls away perfectly without the MAF connected and there is no puff of smoke(black fuel smoke) but it struggles at top end.
Notice I didnt say "New MAF".

I thought I had found the answer but now I am unsure. Should I splash for a new Maf or shouyld there be a fault code if that is faulty.
Just to re-cap, with the old maf connected, there is no torque when you pull away but with it disconnected it pulls away perfectly. There are no fault codes showing whatsoever with VCDS.

Any ideas Crasher?

[Crasher]

The way I deal with this at work is my old adage "no codes, no power, new Air Mas meter" (AKA MAF) AND I will only fit genuine VAG AMM's. Assuming this is a manual box AVQ engine, VW offer an exchange unit under part number 038 906 461 BX which is £144.23 all in. IF this fails to solve the problem, which does happen (I have had a few new genuine AAM's faulty out of the box); then it starts to get a LOT more complicated, requiring in depth measuring block and output tests work but to have this symptom with no codes and a new AMM is pretty rare.

[gkm24]

Thanks for the reply Crasher. I must say that I did not fit a new AMM but a secondhand one. I just took it out for a test with measuring block 11 and with hard acceleration the AMM is measuring over 900 and sometimes over 1000 so im not so sure the AM is faulty. I will check all vac lines and report back. Under hard acceleration it holds back and then takes off really well with a puff of black smoke with the AMM connected but pulls fab from idle, no smoke but with no power at top end with it connected.
Anyway, going to check vac lines.

[Crasher]

Trying to diagnose a faulty AMM is almost impossible by studying the measuring blocks. On the latest common rail models the ECU has a built in AMM plausibility test but it never seems to complete... just keeps running. Something else that worries me, the two values I use in Measuring Blocks Zone 011 are 002 and 003 which are requested and actual boost pressure so after a road test has produced some nice spikes I can pause, return and show a non technically minded customer a nice clear graphical illustration of an overboost condition by logging it in graph form. The measuring block group for the AMM is 003.