Odd behavior after new MAF


Veteran Member
Sep 28, 2005
'98 NB, '04 Jetta
I put a new MAF on my bug the other day, and something odd is going on...

First off, car is WAYY faster than it has ever been. I bought this car from Dan Simoes (TDIparts founder) at 98k, (now 250+) It has had the same Sprint 205s, and Upsolute Stage I for most of its life. It was always quick, but not like this.

The other thing it always was, is smokey. Which Charlie (Kerma) told me was inevitable with the Upsolute Chip. Anyway, now with that new found power, it smokes a lot more as well. And I mean a lot. Under WOT, it is ProStock International Harvestor style soot :eek:

There is also a weird boost leak sound at what I would consider to be around full boost. I dont have a boost gauge so I dont know the exact range where the sound happens, but it is definitely when the turbo is close to fully spooled up and only under a load...

The sound is just like a hissing style BOV on a big turbo sports car :confused:
Only makes it under load and at pretty much full boost "FFFFT FFFFT FFFT"

I dont see anything I could have disturbed when replacing the MAF.

Where do I start? I know @ 250k it wouldnt hurt to replace the Vacuum lines since they havent been done, but I dont think they are at fault here with it beeing soo much stronger.

I dunno, I am stumped.

Any ideas?


Top Post Dawg
Aug 2, 2007
Chapin, South Carolina, USA
2005 A4 Jetta 5spd
It sure sounds as if you have a boost leak. I would start by inspecting the hoses and pipes that carry the boosted air from the turbo to the intercooler and then to the intake.

The high air flow that the leak causes the MAF to see allows beaucoup fuel to be injected, but the cylinders are seeing low air flow, and severe smoke results.


Veteran Member
Jun 29, 1999
Simcoe County, ON, Canada
2010 VW Golf Wagon 6MT Highline TDI
You have a boost leak for sure. I had the same noise once, after the dealer forgot to reconnect the hose from the turbo to the intercooler, after replacing accessorie belts.