The clamp for the air intake boot to air flow meter/throttle body may
yield tension and could cause a vacuum leak.  This may create a lean
running condition resulting in the engine to idle rough and in
severe cases stall while idling.

Installation of Boot Clamp Part Number 191 129 647  will correct this
condition.
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from Service Bulletins, Model Year 1987
.......................................................................
Tech News 87-N05
Issue 5, May 1987
Easy Does It

When removing the cross-over water pipe on a 1982 through 1985 model 1.9
liter Vanagon waterboxer engine ... you have to use care.

The cross-over pipe is secured to a welded stud on the intake manifold
(arrow) that could break or crack.
<picture showing engine from rear of car>

If this happens, a vacuum leak could develop that would be hard to
detect. Such a vacuum leak could cause poor performance under all
running conditions due to leaning out of the mixture ... and would
occur even when all other systems are go.
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Technical Information
Group:    28
Number:   87-04