Unusual problem with LH 2.2 system

[James Weiler]

Just as guess but have you checked the throttle position sensor?  It 
sounds like when you close off the throttle the engines is still too rich 
so I'm guessing the ECU doesn't know you've backed off.  There are no 
detectable divability problems probably becuase the system works well 
enough on just air flow and RPM signals alone.
Just my $0.02 worth.  Let me know what it was when you figure it out. Don't 
you hate it when people say that :)

jw