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RE: S4 Cold Running Problems

I'm with Bob.  Likely suspect: Bent valve.  In my "youth" (mid-30's),
after turning FTD at
the local autocross club (with a well modified 1.6L Jetta making about
100 hp and electronic (Allison InfraRed) ignition and no rev limiter), I
felt obliged to race a mid-70's Trans Am off a green light.  Probably
revved the poor little 4 banger to about 8 grand (no point float or
valve float to stop me) before I shifted.  No problem. (I lost before 3
rd gear).  Car was running fine when I shut it off in the carport.  Went
to sleep feeling smug.

Next morning, with the engine cold, it ran like sH*t - very rough, no
power, banging away.  I suspected valve problems (55 Dodge experience)
and immediately pulled the head off and took it to a local shop.  I
can't remember if we could tell which valve it was or not but bottom
line: one exhaust valve (probably with a week spring) had apparently
failed to get out of the way of a piston at 8 grand.  When the suspect
valve was rolled on a flat surface it did a nice little undulating
dance. Oops (or Doh!) Very cheap to fix tho'

My suggestion: check the cold compression - a bent or slightly burnt
valve will likely show low compression until the motor warms up and some
of the tolerances (and gaps) close up. Of course, if I'm right, the fix
will not be as easy as it was on the 1.6L four. (Doh!)