Cadillac: 1992 Cadillac DeVille, valve stem seals, combustion chambers

Question
To Whom It May Concern:
  I have a 1992 Cadillac Sedan DeVille that tends to run rough at start after it has been ran for awhile.  When I start it in the morning, it runs very smooth.  However, after it has been driven for about 10 miles and then it is turned off, when you start it again it runs rough (sometimes stalls out right after the engine turns over).  After it is back on the road again, it blows a small puff of blue smoke out the back when it first starts off and then it runs great and idles fine at lights and stop sign (no more smoke is blown out either).  I have had the distributor cap and rotor replaced, replaced spark plugs, had a full tune up.  Any suggestions?  Could it possibly be the oxygen sensors?  I know it is old and doesn't run like brand new, but when I say it runs rough, it is pretty rough.  Thanks a lot.

Answer
That PUFF of BLUE smoke is an indication of engine oil leaking into the combustion chambers of the engine.

Probable caueses are :

1. faulty valve stem seals.

2. Faulty oil rings on the piston(s).

This would explain your rough running engine, as the oxygen sensor(s) are seeing this oil dilution in the exhaust and causing the fuel to become much to lean for the engine to run properly.

Once the oil has been exhausted the engine runs back to it's normal condition.

autohelp