Been working on my son's A3 and have learned lots from you guys. What to do and how to really screw thing up if not careful. Biggest issue was crappy fuel and stuck check valve on the return line. got that fixed and she runs good. Now got to learn about the air/compressor system. Seems the drivers side may have some sort of blockage as the CTIS doesn't inflate the tires on that side and the rear air line for trailer hook up does not supply air when the valve in opened.
Again, thanks for you advice.