moedip - I really appreciate your advice.
the clacking sound goes in cycles - comes and goes. Warm or cold.
This car has 98k miles....
I've been reading Mike Tangas's adventures of rescuing a 560 from the junkyard. Quite amazing.
You think I'd be able to find an appropriate filter at TrakAuto?
One thing I know is if you've got one problem, you can usually get to it deductively. If you have two, you'll go crazy. My next steps will be:
1. check the wires at the idle control unit
2. install a clear fuel filter (also to monitor condition of the fuel line)
2. clean the idle air valve as you described
Any way I can test the cold start injector? In one post on this site a person pulled it, left it attached on the side, and then plugged the hole (of course with the car completely warmed up), and then started the engine.
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)