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Re: Deceleration

On Wed, 14 Jan 1998, Martha Stump wrote:

> 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.  

This is normal, I think.  My CQ does this, and I've seen it on BMWs with
trip computers.  What happens is that on MPI fuel injection systems, the
computers "cut" the gas on deceleration (at least as far as I understand).
The side effect of this is that the MPG computer no longer has all the
parameters to calculate MPG (one of which being fuel flow...), hence the

Some BMWs have a "consumption" gauge thing below the speedo, and
this does not happen, but that thing only measures vaccum in some fashion.
The trip computer is a slightly more sophisticated device.

> Accomponying this is a serious lack of engine braking.

Er, this is probably a different problem or perhaps just impression.

> 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!!!!!

That is probably a dirty ISV.  I think there is an FAQ about that on the
list archive...

'90 CQ (looking for a low miles dark '91 CQ)
'87 RX7 Tii (for sale soon)