90 Coupe Quattro - Bad ECU

[JRheeman@aol.com]

Hello fellow quattro owners,

I've been enjoying this list for quite some time now.  Fortunately for me, I
haven't had any real problems with my 90 CQ until recently.  My car had been
stalling whenever I coasted to a stop.  I saw that some other people were
experiencing similar problems.  There was much discussion about a bad or
dirty ISV.  So, I took mine apart and cleaned it per some listers'
suggestions.  Since then, the car has been stalling even more frequently and
it is definitely running very rich.  I took it to a mechanic I trust and he
did what he could, but he doesn't have the equipment to diagnose the problem.
 He did find a vacuum leak.  The idle had also been searching, but this has
now subsided.  However, the idle is now running high and it fights me under
braking when the engine is around 1200-1300 rpms.

This week, I dropped the car off at another shop that I trust only on faith.
 I bought my first CQ (totalled - oops) from this guy.  I had my 60,000 mile
service (including rear pads/rotors and timing belt) done there as well.
 Other than a K&N air-filter from Schaumberg, I've only changed the oil on my
car.

Well, this morning, they told me that they ran a diagnostic and the fault
codes are telling them I have a bad ECU.  They want $800 for a new one or
$350 for a used one, plus $187 to put it in.  Can anyone tell me if this is a
common problem.  Does this make sense?  If I fix it, is there a good chance
that I still have a bad ISV, Mass Air-flow sensor, or O2 sensor?  Should I
take my chances on a used one, or go with a new unit?  Should I buy one
elsewhere and put it in myself?  They already have 2 hours into the car, so
it almost makes sense to have them do it, if this is really my problem.

Any advice on this matter will be greatly appreciated.  I have to let them
know what I want them to do pretty soon.

Thanks again,
Jason Rhee
1990 Coupe Quattro (Red/Black)