Hi guys,
We recently bought our first VW, a 2000 Golf 2.0. Happy with it for the most part (seems built like a tank), but she's blowing an awful lot of black smoke. Black is better than blue at least.

I took it up to our local VW mechanic (Autohaus at Hornsby, I highly recommend them) for a quick diagnosis. It was Christmas eve and they were having a clean up day. He didn't really have to help me but he did. Anyways, I suspected O2 sensors, but they came back with no fault codes. The mechanic suspected a MAF sensor and replaced that, as well as resetting the computer. It made an improvement to be sure, but the fuel economy is still awful and under high revs she blows jets of smoke worse than the filthiest diesel I have ever seen.

I have replaced the air filter and spark plugs. The latter were badly carbon fouled. Today I took the car to the dealer (as it's still under warranty, phew), and had another diagnostic done.

Still no O2 faults, but it is reading multiple misfires, and saying it's running lean. Which explains why it's dumping so much extra fuel to try and enrich the mixture. SO.... am I right to assume the O2 sensors are indeed faulty, but just not telling the computer that they are?

I'll be taking the car back to our mechanic on Monday morning and giving him the story, just wondering if anyone has some ideas and what else it could be.

Cheers in advance!