[s-cars] electrical problems, now no boost

[otw185]

Here's the story:

Drove my 92 about 2 hours last week to my mechanic for
a suspension upgrade and samco hose and new diverter
valve from audi TT 225.
1) Mechanic said car would not start after 2 days
sitting and gave small charge jump with portable
charger in order to get into the shop.  Work
completed, everything OK per mechanic.
2) I drove 2 hours back home a few days later. No
problems. Next morning car dead again.  Dead means
some elec. there, but got the clicking sound when
turning the key over.
3) I ran my portable charger on it (low setting, 2
amps) for 20 minutes which gave enough juice to get
the car started.
4)  no more problems for a week.
5)  all of a sudden, one afternoon, all power windows,
except driver's!, are inoperable using any of the
switches.
6)  Next morning car won't start.
7) Ran my charger for just a few minutes, car starts
and windows all work fine again.
8) Today, go off to work and the car feels a little
faster than normal.  I get on the highway and car
boosts nicely
9) then all of sudden, a huge lurch (like fuel cutoff,
or feeling of hitting rev limiter, but at 3 or 4K).
Giving throttle a few more times gives the same strong
hesitation at this tach range.
10)  Now the boost gauge reads a constant 1.1 bar with
car running, but absolutely no boost.  No funny sounds
under throttle, no audible air leakage, no black
smoke.  Just runs like a 5 cylinder car with no turbo.
 Very smooth, no idle problems.  The lurching is also
gone.  Shutting car off with key still in ignition,
gauge returns to 1.0 bar (sea-level ambient) like
normal.  I smell nothing funny, see no smoke and can
see no signs of hose release or breakage.
11)  Battery is original.  I plan to replace (is
aftermarket advisable or should I get it from Audi)--


anyone have a clue what's up???  Fried ECU from the
charging?  Battery old and causing low current
anomolies such that ECU shuts things off??  Really
weird.  Car is otherwise perfect with only 45K miles
and all maintenance ahead of schedule, mobil 1.  Prior
to this, boost always smooth and runs to 2.1 bar.  Car
is unmodified excepting the hoses and new diverter
valve form audi TT 225.  I checked out frequency valve
connections which appear to be in place.  Have just
learned there is a fuse which controls this valve and
plan to check later....

Thanks for reading.
Scott
92 S4, normally aspirated.


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