2006 Jetta TDI 300,000 miles sudden loss of MPGs.

[Rolling_Coal]

So I've owned my TDI since 241K and just recently turned over 300k and had the timing belt replaced at a reputable shop around here. Turbo condition is unknown. Maybe original. Car has been running fine but recently I feel like I've had to fill up more often than usual so I calculated my MPG using the same methods I've always used and yea seem like I'm only getting 390ish miles per tank or around 28mpg. I have always got 45mpg. This is a mixed of city and some highway. I recently moved to Texas the last 6 months and don't drive hwy as much but i don't recall getting that low ever...I drive her pretty easy.

I've searched and search and read about turbos going out but I have some not much black smokes between shifts, some oil in the intercooler piping. Last oil change was a 2 quarts low but It's always used a bit of oil. But nothing unusual about all of these things. I don't have any noticeable loss in power but I do notice sometimes a hiccup accelerating around 1800 rpms. I've checked all both upper and lower intercooler fittings are seated. They have some wiggle room but are seated. Maybe worn o-rings. I do have Torque light and a bluetooth OBD2 and boost is reading 12-18psi and intake manifold presssure replicates rise in boost. Not sure how accurate it is.

I'm so confused because car drives fine. No noticeable smoking. What do you guys suggest I do? I don't know if just throwing $1000 and replacing the turbo is going to cure it or not. How can I know what to do? No codes either. Last code was 3K miles ago and was stuck throttle actuator which I've replaced and code went away.

 

[Rolling_Coal]

I can't find where to insert pictures on here but I did just find that the hose clamp right downstream of the MAF wasn't clamped where it goes. Hose was connected. Do you think it could possibly draw enough vacuum to pull air from that location? Bypassing the MAF?

 

[Mach1]

That induction leak could be your problem, Maf needs to operate correctly by having a sealed induction tract to achieve proper fuel economy. I would also ask since you had the TB done, did they set the timing? This is another huge factor in achieving max fuel economy.

 

[Rolling_Coal]

I can ask them if they changed the timing? Let them know the situation Maybe it's doesnt take much to check. hwy driving for just a few gallons got me 38mpg average but not the 45 i was at constantly

 

[1998993C2S]

Correct me if I'm wrong. Removal & replacement of the 1.9l BRM timing belt procedure requires an ignition timing adjustment. Better said, ya can't do a TB it without. ...