the car doesnt exceed 2800 rpm

hi friends, as suggested i had disconnected the MAF & drove there is lot of improvement,its back to full power and to my surprise no smoke,earlier it use to smoke up a bit.do i run like this ?does it harm ? what is the end result is the MAF dead ? shall i replace with a new MAF or try cleaning? bye

It most propably is not back to full power. It may seem so if the previous situation was almost no power at all.

Disconnecting MAF causes the ECU to use a default value for the Mass Aif Flow. This means that no more fuel is injected when the turbo pushes more air into the engine. The ECU cannot see this, hence full power is unavailable. At high rpm the turbo is pushing more air into the engine than the MAF default value is. This is why there is no smoke.

Driving with the MAF disconnected should not directly harm the engine. I am not sure what happens at the Exhaust Gas Recirculation when MAF is disconnected, but I would assume that the EGR is turned off. This would mean more NOX in the exhaust gas. So basically you are just lacking full power and polluting some more.

One thing to consider is your turbo vanes. The variable vanes do tend to get stuck if the engine never sees higher rpms. This could be one explanation if you are really getting good performance with MAF unplugged. Unplugged MAF turns boost control to minumum, but if the vanes are stuck (they always stick in the full boost position) then you would have all the low rpm grunt still present.

This would actually be quite likely if the MAF has been bad for a long time. The bad MAF tells the ECU that there is very little air flow, so the ECU keeps the boost control at max all the time. You also do not get the overboost ->limp mode fault since the bad MAF will also limit fueling and keeps the revs down. If the boost control is requesting max boost all the time, the vanes wont move and they are prone to sticking.

Once you get the MAF cleaned or changed (Easy DIY) you can try accelerating with pedal to the metal to the redline. If that makes the boost disapppear, then you have a dirty turbo too. It can be cleaned, but that is a bit bigger job.

You can get an idea of the job if you read one more TDiClub HowTo.

Vesa