I have a 2001 Audi A6 it starts but does not drive, the mechanic told me it would cost around 4,000 to fix and that it was a computer problem. What I want to know is if I can just buy an ECU just say off of ebay or craigslist and just unplug the old one and plug in the new one, kind of like you can do with Honda's? Is that possible? or will it really cost 4k to fix