V8 hard-start/stall/stink/now OK

[jackr@internet.kronos.com]

 I have weird Audi behavior that I can't explain.
 
 Tuesday morning I start my V8.  It starts as normal, but stalls after a 
 second.  Uh-oh.  I have trouble restarting it.  It stalls.  Repeat, giving 
 it gas and keeping it running several seconds.  I'm late for work, so I 
 take a different car.  (It's nice having spares!)  As I get out, I smell 
 over-rich exhaust.
 
 Wednesday morning I repeat the experiment.  It starts and stalls.  I start 
 it with difficulty and keep giving it gas, keeping it running several 
 seconds.  Lots of smoke pouring out the exhaust.  It looks blue in the 
 morning sun, but a check of its odor indicates it is mostly soot.  I start 
 it with difficulty again and keep feeding it gas keeping it running. After 
 about 5 to 10 seconds it stays running on its own.  Lots more stinky 
 exhaust from the initial poor running, but now it seems fine.  I drive it 
 around the driveway and a short distance up the street and all is back to 
 normal.  I have an extra-important appointment so I take a different car.
 
 Thursday "It's a good day to get stranded", so I drive it to work, and 
 again at lunch, with no problems.
 
 Any clues?  Oxygen sensor is only a few months old.  The old one went 
 suddenly, leaving the car completely non-startable (due to excess gas) 
 with no advance warning.  Is it about to repeat?  TIA.
 
 Jack Rich
 90 V8Q
 88 Corvette convertible
 84 4kq