New TBV - no more dyout AND no more bucking

Phil & Judy Rose pjrose at
Mon Aug 6 20:27:42 EDT 2007

At 03:17 PM 8/6/2007, Steve Scalmanini wrote:
>I hadn't known that a defective TBV could cause major bucking at
>moderate to high boost, but when I replaced mine it solved both that
>problem and the commonly known die-during-hot-idle problem.  Is this
>news or commonly known?

Well, what _is_ news to me is that the TBV is associated with what 
you call a "die-during-hot-idle problem". I've read hundreds of posts 
over the years about defective bypass valve symptoms, but never that 
one. The valve was designed to avoid a sudden slamming shut of the 
throttle plate when under boost and coming quickly off throttle (a 
common example is accelerating with significant boost pressure and 
then suddenly lifting and braking to a hard stop). With a 
malfunctioning TBPV, the boost pressure can slam the throttle plate 
tightly closed and starve the engine (so it stalls). I've never heard 
of the TBV in respect to simply dying "during hot idle". Why would it 
cause that, I wonder?

As to that other symptom: bucking under high boost: I assume that 
could be caused by any manifold pressure (hose or hose clamp) leak so 
that may happen at one of the hose connections to the valve of it's 
too loose (valve defective or not). When you replaced your TBV, you 
probably also got better (tighter) hose clamping as an "extra" benefit.


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