Routine timing belt service has turned into an ongoing troubleshoot for why it now sounds like a diesel running. Have had the job redone twice with all new parts to no avail. Going back to the dealer this month for them to replace the belt again because they think there is some issue with it.
A/C head failed. Very simple to replace on the 92-84 cars.
Hydraulic leak proving hard to trace. Rack was replaced at about 70K according to records.
Battery discharge problem finally traced to corroded main ground to chassis.
Motor and transmission mounts replaced.
Speed sensor failed.
Cruise control is now intermittent.
The usual Audi window switch failure. Easy to fix once you know how.
Power recline for driver's seat failed.
Mass airflow sensor failed. Easy fix, expensive part.
Poor gas mileage. 16mpg city and 19 highway. You can push it to 21.5 but only on a carefully controlled highway-only test.
Great highway cruiser. Comfortable, seats are terrific. Best at high speeds which is ironic because where can you do that anymore!
Not particularly quick despite the 4.2 engine. I had a 1990 V8 with the 3.6 engine and they are positively sluggish believe it or not. My Audi 200 turbo did better than the 3.6. The 4.2 is noticeably more zippy than the 3.6.
The most salient point about the V8 Quattros is that the 92 through 94 version is much improved over the 1990 and 1991 version, most notably with the better engine, improved suspension, new climate control system, remote entry and other tweaks. I've had both and would never buy a 1990 or 1991 again, but the 92-94 years are still of interest to own.