re. 4000Q Stalls when I let off the gas

[Ben Swann]

Many things can get you to this poor running.  Injectors aren't necessarily the problem and they are expensive, so try the simple and inexpensive first.

Replace the air filter as a matter of course and while doing, verify the air-flow sensor plate is not binding.  I frequently find that some dust or grit gets lodged around there, usually the car needs a tune-up at this point.  The plate will bind or stick causing the car to stall.

If the ISV does not seem to be working right, a few things to verify:
1) Idle witch working?
2) ISV operating as it should?  Sometimes cleaning helps, but don't stick anything in it or you will likely tear the rubber seal.  Better to use throttle cleaner as it will not break down the rubber like carb. cleaner.

Check for vacuum leaks and repair as needed.  A tunup including distributor cap and rotor may be in order.

Getting more involved, you may need to pull the injectors and replace the seals.  Do a spray pattern test  - insert orange relay in place of fuel pump relay and turn ign. on then lift plate in order to get injectors to spray.  A nice conical spray  - even across all injectors is what you would like to see.  Replace any that are bad   What usually is the fix is new viton seals however.

Clean up the ground to the manfold.  Sometimes a good throttle body clean is in order - need to remove to do this properly.

Ben

[From: Liotta <rliotta at alaska.net>
Subject: 4000Q Stalls when I let off the gas
To: quattro at audifans.com
Message-ID: <41FB3594.286574AD at alaska.net>
Content-Type: text/plain; charset=us-ascii

Hello all--

I have a 1985 4000S Quattro.  135,000 miles

It runs pretty good at speed, but when I let off the gas (in neutral),
RPMs fall below idle speed and it frequently stalls.

In recent past I have monkeyed with mixture and idle speed -- because it
was  idling rough---  and now is smoother but --- it will still stall--
so I increased the idle to 1100 or so.  This brute force method helps
the stalling but---- is pretty lame!

My mechanic says I need new injectors--- I have already tried injector
cleaning solutions.

Do you have any ideas???

Thanks very much----


Rick]