I have an AUM MK4 1.8T and have fixed the secondary air intake and starter over run. Its had a new dump valve, air filter, MAF, N75, Bank 1 Lambda sensor and its now doing my head in. No fault codes.
Seems ok most times from cold, but when warm its lumpy between 1 & 2k RPM.
What could this be, or does anybody want to buy it as I am done with guessing.