The Mass Air Flow sensor is the sensor that sticks out of the pipe leading from the air cleaner box down into the intercooler. Google it and you should see lots of pics which will show you exactly where it's located.

 

I have a 2004 1.8T quatro. You are describing similar problems as to what I had.

I found the 90 degree elbow out of the crankcase that fits into the PCV have sheered off ... it was a total pain to fix but that resolved by poor idling issues.

 

What PCV means?

 

I found where is the MAF located. I will verify the condition in the next few days...

 

and I found what PCV means..I will check that also.

 

How long have you had the car? Has it donne this the whole time you've owned the car?

 

Since 1999. No.

 

I cleaned the MAF Sensor and re-adjusted the Snub. I still have the same problem. When I put the car in PARKING or NEUTRAL, the car is smooth, no vibration at all. The car vibrations stop. But when I put the transition in DRIVE, I noticed that the motor pivot to the back of the car. It seems that this rotation is causing that the transmission mount hit the car transmission mount base and the motor vibration is transferred to the whole body. I changed the motor mount twice and the transmission mount are new. If I change the transmission in REVERSE, same scenario. The motor is having a think too much back and forward movement. Does any body know how to avoid this motor pivot movement? Is it normal?

 

Check for something loose around the tranny. The transmission mounts play a role in the foreward and backward movement of the engine. Also a bad tranny mount. Maybe a missfire under load? Any codes or lights?

 

Car was scaned. no codes. I still have the vibrations. I am planning to change again the engine and transmision mounts but now I will replace them with OEM(Genuine Audi) mounts. The actual ones are from FEQ. I am noticing that the engine is moving foward and backward too much when I shifting from Drive to Reverse. As a note: When I turn off the AC the vibration is reduced by 50% but once I turn on the AC, the vibration retuns. It seens that the engine is receiving more load from AC compresor and moving backward the engine. Any other suggestion will be apreciated.