Intermittant stall on coast-down

C1J1Miller at C1J1Miller at
Thu May 1 23:03:49 EDT 2003

It's a bad turbo bypass valve, also called a throttle overrun cutoff valve. valve

Replace with stock bosch part for around $35 or so, or get a fancy metal
aftermarket unit for triple that, which lasts longer and is serviceable.  I'd
stick with stock on a stock motor, for sure.

Chris Miller, Bolton MA USA, c1j1miller at
'91 200q20v ==>
I have a '91 200 which has begun to intermittantly stall as engine
approaches idle rpm in coast-down situations (i.e., braking with clutch in).
Promptly restarts by letting out clutch (if car still moving), or by using
starter.  Engine is fully warmed-up when this happens.

Had an identical intermittant stalling problem early-on while the car was
still under warranty. It stumped the dealor, and the Audi field support
staff, so car was eventually sent to the Audi emissions/engineering facility
in Southern California (I believe Agoura or Thousand Oaks), where they went
through all the possibilities and finally located the problem, which was a
perforated diaphram in a vacuum-operated control device they had not
previously encountered a failure with. (I wish I could remember what
component that was).

Now, 10 years later, I am experiencing the same stalling behavior ... may or
may not be the same cause. My mechanic, who worked many years for the local
Audi dealor, and now is independent, replaced the fuel pump relay switch (as
he had experienced this to cause similar problems), and has also gone
through all the vacuum lines to rule-out obvious vacuum leaks.

Recommendations on what to check or do next?

Thanks, Kevin

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