87 5KT: vibration and hard starting

[Aleksander Mierzwa <alex@matrix.pl>]

Hi List,

It's probably a long time since I last reported any serious problems with
my '87 5KT, so today it's double shot ;-) I need advice.

1) Since I bought the car it was vibrating at idle. The vibration is worse
when you put the transmission in drive and gets really annoying when you
turn on the A/C (sometimes you can actually see the steering wheel shake).
I was blaming it on old engine mounts (though they looked OK). Finally,
this weekend I managed to replace both of them with new Boge (OEM) units.
Replacing LH one was prolly a waste of money - old mount looks like new. RH
one suffered from the "Scott Mockry" failure mode - the mounting bolt
separated from the mount itself. Fitted the new mounts, tightened them with
the engine warm and idling. Guess what? The vibration is still there and
isn't any better. I'm really stumped now. Is this a problem with the engine
mechanicals (like bad crank bearings)? The vibration is not associated with
any noise, it's just this - a vibration. It disappears when you rev the
engine beyond 1500rpm. Maybe I have a fuel/ignition problem (unequal fuel
delivery between cylinders causing the engine to go out of balance at
idle?). I'd really appreciate any thoughts.

2) This one is more annoying. Since maybe a week I'm having problems with
fuel system. When the car is cold, it doesn't want to start - idles very
rough then dies, requiring several starting attempts to finally run.
Running the output tests to run the problem doesn't help, so it rather
rules out lack of residual pressure. Fuel pump is ~6 months old. When it's
warm, it starts but idles low and hardly reacts to throttle - it runs
smooth, but feels like it has maybe 50hp intead of 162 it should have. This
behavior lasts for 3-5 minutes and then _suddenly_ everything goes back to
normal - it's like someone flipped a switch. Once this happens, the car
runs well until you switch it off and start it again after some time. The
whole problem does not happen every time. Today I guess I found the
immediate cause - the frequency valve refuses to work for couple of minutes
after starting the car. What's more bizzare is that at the same time the
radiator fan refuses to start in 1st speed when the A/C is on and instead
cycles on and off at medium speed in a weird pattern. Seems like some crazy
electrical problem - where do I start? Is this a symptom of failing
manifold grounds Phil so often speaks about? Again, any input will be
appreciated.

Aleksander Mierzwa
Warsaw, Poland
mailto:alex@matrix.pl
87 Audi 5000CS turbo (mine)
88 Renault Medallion wagon (mom's)
91 mountain bike (just in case both cars break at the same time :-)