Deceleration

[Martha Stump <tree@triton.net>]

My '89 80 quattro is having a very strage problem. 
When I let off the gas to decelerate (or after downshifting), my trip computor,
when set on the instant mpg, will normally only show dashed lines. 
However, occasionally it will show the same mpg that the car would get
if I took it out of gear.  Accomponying this is a serious lack of
engine braking.  There's no reason that I can tell as to why this
happens (the car seems to be randomly annoying me) and in addition, my
car will sometimes idle anywhere from 1100 rpm to 1800 rpm (normal is about
800).  Any ideas on what's wrong or how to fiw it?  Much thanks
in advance!!!!!

Mike Stump

'89 80q