Alh problem 03 Jetta TDI wagon

[vwman2]

Hey all,
Recently at about part throttle under load my Jetta feels like it hits a flat spot and at that same time a large amount of black smoke will pour out. Also don't know if it's related but when I shut it off I hear a hummmmm sound for a few seconds. If I were to floor it seems to not do the flat spot but part throttle with a little load triggers it. Turbo only has around 90k since it was replaced, car has almost 300k now. Maf is good fuel filters always changed ever 10k by me. Not sure what else to do. Car is tuned with Malone stage 3, nozzles were done at time of tune also
Thank you all
Jamie

 

[panthers89fan90]

.

Hey all,
Recently at about part throttle under load my Jetta feels like it hits a flat spot and at that same time a large amount of black smoke will pour out. Also don't know if it's related but when I shut it off I hear a hummmmm sound for a few seconds. If I were to floor it seems to not do the flat spot but part throttle with a little load triggers it. Turbo only has around 90k since it was replaced, car has almost 300k now. Maf is good fuel filters always changed ever 10k by me. Not sure what else to do. Car is tuned with Malone stage 3, nozzles were done at time of tune also
Thank you all
Jamie

Do you have a VCDS? Can you take a log of requested and actual boost?

Is your timing advanced?

Is your snow screen clean of debris?

 

[jettawreck]

"MAF is good". Make real sure.
Unplug the MAF and see if it gets a bit better. If better or about the same, pretty good chance the MAF is bad. If working properly, it should preform noticeably better when it's connected.
If you have/access to VCDS, you could log the actual vs requested values to verify.
Not all MAF failures act the same. My 2003 had a "flat" spot and smoked. The others mostly just acted lethargic.
Other than that, if you are certain you don't have boost issue (vacuum leak, etc) it sounds like injector issue. Where is the timing set??

 

[vwman2]

Thanks all for the help so far.

MAF is just a few weeks old as that was my first swag ät it. Timing belt was recently done by a local guru but problem was there prior.I was hoping it was something with timing. I did not have a lot of money at the time to have more labor to diagnose. I can get my hands on a vcds to see what boost is calling for and what its getting.