5k stumbling solved!!! - long

[Bill Lockwood]

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Hopefully this may help some of you 5k owners out there, since many of our =
cars have many of the same problems at the same times.

Many of you had heard my plights about my 1988 5000 CS stumbling at part th=
rottle while cruising.  After many rounds and failed attempts, I have found=
 the culprits.  Each fix helped a bit, but only one really fixed the proble=
m=2E  Fortunately the intermediate fixes were made, because otherwise, the =
car would have been "fixed but not quite as fast as it was."

The problem: When starting, the engine cranked for a long time, started mai=
ntained a low idle, or wouldn't idle.  Once warm, idle was rock solid ~800r=
pm.  When driving away on a cold motor, bucking would occur if gas was not =
applied gingerly.

When cruising, the car would stumble.  Especially noticeable at mid rpm 3-4=
k, worse if you could get it higher, in low gears.  Problem worsened after =
a high load stint of driving.

Under boost the car would pull hard, but still felt a little soft.  Turbo w=
ould sound spooled before real boost was built (12 psi).

Fixes:

After pulling the codes, an rpm sensor was faulty and replaced.  Marginal i=
mprovement in starting and driving.


Replaced fuel pump with a used unit.  Old one was very noisy and at least ~=
6 years old.  No improvement.

All Michelin man and other large hoses checked.  No problems.

Unplugged oxygen sensor, no change except very doggy throttle response.

Checked intercooler, this was a problem. IC o-rings had been leaking under =
vacuum and sealing (almost) under boost.  Oil misting around the end caps l=
et me know about a possible problem.  Tested IC in sink with soap, end cap =
seams blew bubbles.  IC had been strapped since boost was raised from stock=
, 3 years ago.  Car started and built boost readily, part of the problem wa=
s solved.  Stumbling still existed.

Under a dark night sky, hood open watching cherry red exhaust manifold cool=
, noticed once EM was no longer glowing, that plug wires were arcing everyw=
here.  Plug wires are ~6,000 miles old.  I am assuming after replacement of=
 cap, rotor, and wires, everything will be fine.

Thanks to all who have helped, advised, and questioned.
It feels good to be back in "my Audi" again.

Bill Lockwood
5ktq "part time lover"

Burlington, VT

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