Turbo bypass valve, blow by blow.

[Phil Rose <pjrose@servtech.com>]

A few months ago, Wolff spoke the following words of wisdom:

>Date: Wed, 29 Oct 1997 21:37:56 -0800
>From: Wolff <wolff_b@ix.netcom.com>
>Subject: Turbo Bypass valve datapoint.
>
>I had the classic intermittent stalling on decelleration on my '91 200
>tq. I checked the control hose for the turbo bypass valve that runs
>behind the heat sheild and 4" inches of it were completely destroyed.
>New hose made no difference in performance.

>I sucked on the control line
>to the bypass valve and got flow. Blew and no flow. Got a new bypass
>valve and you can't blow or suck air through the control port. Installed
>it and so far no stalling and the engine rpm's fall more slowly during
>shifts making driving much more smooth.
>Wolff
>'91 200 tq

I have a question about the '91 200q turbo bypass valve. Although I don't
have any stalling problems (intermittant or otherwise), the turbo lag does
seem somewhat  more than I recalled from my previous car. The bypass valve
control hose was replaced just before I bought the present car, so is not
suspect. When I tried the "suck and blow" test that Wolff described, I got
the _same result_ as he did. Is this result generally agreed to reflect
*faulty* operation of a turbo bypass valve?

The Bentley manual says to apply/release vacuum and observe (visually I
guess) that the valve opens/closes. It's not clear that what Wolff (and I)
observed is necessarily an indication of a failed TBV. Any other BTDTs?

Questions on the hose itself: The OEM hose was replaced by a plain rubber
vacuum hose. Any reason why the OEM hose has/needs the cloth cover? BTW, I
seem to recall others posting about rerouting the bypass valve's tubing to
pass around the _other_ side of the engine; is that correct?

Phil Rose		Rochester, NY
'89 100
'91 200q		pjrose@servtech.com