I have a 2000 A4 1.8L tubro, runs really bad at start up for a minute then smooths out and idles perfectly. But when I place it in gear to drive off the engine stumbles and begins to register codes 300, 301, 302 303 304 All represent cyilnder misfire. Also rich at idle but then long term lean 1138 and 1130 respecfully. I have replaced, air filter, fuel filter, fuel pressure regulator and suction jet near the intake. Mitchell on demand service program suggests presure sided air leak between turbo and intake. I have replaced or examined air ducts between the two. Still registers mis-fire and lacks power. I can drive and achieve highway speed by pulsing the accelerator pedal. I am thinking bad throttle assembly, ouch $600 guess!!! Any thoughts???

 

Try to take of the oil filler cap when the engine is running. Will it come off or not?