GDI Tech

Can you remove the intake manifold and look into the intake ports at the valves? I may be mistaken, but I believe the 2003 1.8L was Audi's first direct injection offering in the 4 cylinder, and severe valve coking will cause what your describing. A leak down test is more accurate at pinpointing the weak cylinder(s) and just where the compression leak is (valve, rings, etc.) by listening. Is it hissing out the intake? Intake valve. Exhaust? Exhaust valve. Crankcase? Rings.

Here is an example of a chunk of deposits breaking loose and then getting trapped between the valve and seat allowing PTV contact and a bent valve. Just a slight bend, but misfires were the symptom:



Removing the intake manifold is pretty straightforward and will allow you to see them up close. Please share pictures with us.