Missing Boost-Again

[Trevor Topley]

Hi Everyone,
                    I've been off the list for a few weeks, maybe the
mail at work, but have been reading from the archives.
Finally have email at home so can contribute again.
First, thanks to everyone who supplied info re our trip to Vermont, we
had a great time despite a hefty ticket in NY, got caught following
another Audi, ass-u-me-d he had a detector,(wrong) and losing .3bar
somewhere.

Which brings me to my problem that has appeared 3 times now and has me
baffled.
My 90 200q has been giving me a grin at 2.0bar for many months with no
problems other than a split hose just below the IC, just days before the
bypass valve went on.
My high boost is obtained using a ball and spring manual controller in
the hose going to the lower wg chamber.
I know this is not the "prefferred" method, but the response(almost no
lag), adjustability and $$$ are hard to beat.
The bypass increased the lag slightly but made it easier to drive and to
upshift smoothly, worth the trouble to install.
Then suddenly max boost dropped to 1.7b, and in 3rd as the revs went up
it would drop down gradually to 1.4b, this made the performance
considerably softer.
There were no other drivability problems and it was still fairly quick.
Thinking of the new bypass valve I removed it, no difference.
Couldn't hear a leak, but dialled max boost down to 1.5b while gathering
bits to pressure test the intake tract.
That took a week or so, found no leaks, reset the controller to 2.0bar
and was puzzled that she was back her to previous grin inducing
performance.
Now I'm a mechanical engineering type and not used to things fixing
themselves, but I'll take it when they do, but know it could happen
again, and of course it did. On the way to Vermont it went soft again,
exactly the same symptoms.
When we were back home I removed the wg cap, thinking it may have jambed
open when suddenly hit with 15psi air and was maybe continuously leaking
some valuable exhaust.
I found everthing free, and was really surprised how little effort it
took to move the actuator, which had a solid knock at each end of its
stroke(is it a poppet valve?)
 There seemed to be too much movement for the design of the diaphragm
and thought about adding a stop.
Did add a 1/8 shim under the spring,(stock), didn't expect to have fixed
it and sure enough I hadn't.
Then a couple of weeks later it fixes itself again, I'm happy but for
how long?
Two weeks!! Last Sunday drove 120 miles with 2.0bar to visit Brother, 6
hours later get on the road and it's back to 1.7again!!
I don't have much hair left to pull out, and need ideas, prefferably
easy and cheap.
        regards
                    Trevor Topley
                    90 200q, was 2.0bar w bypass valve
                    83 Honda 650 Turbo, (gives an even bigger
grin)approx 2.2bar, no IC