Hi all; This is my first post, although I've gotten a ton of value from browsing these threads over the past few years. I'm running into an issue that is idiosyncratic enough that I thought I'd check and see if anyone here had ideas. 2004 Golf TDI, BEW engine, 153K (Timing belt replaced at 87K) I've been getting the "mass airflow sensor" code for a long time now. I replaced the sensor, but it didn't solve the problem. I got it checked out and found that I needed a new camshaft; with the help of the walkthrough here, I did that myself with a KermaTDI camshaft replacement. Everything went well and the car seemed to be running better than before, but I've now noticed some other issues--and it's still throwing the same mass airflow code! Here are the symptoms: slow oil leak - This seems to be from the valve cover gasket, so perhaps I installed that incorrectly when replacing the cam. increased engine noise - not at first, but when the car has been going for a while and/or at high speeds, I can hear a louder sound from the engine. It reminds me of a jet engine warming up or cooling down, actually. It's especially noticeable when I'm slowing down coming off the highway. I also recently noticed that that sort of whirring noise increases and speeds up as the car speeds, up, not just when the engine is going faster--I heard it while speeding up in neutral going down a hill. extra black smoke from the exhaust - especially when accelerating, but mostly at higher speeds (40-60 mph) Gas mileage is holding steady, although occasionally it seems like the power is diminished. Could all of this be from a valve cover problem? I'm also suspicious of the turbo starting to go bad. What does this all sound like to folks here? Thanks for your time!