Here is an update on my original post from way long ago.

Original post:
I have a 93 Lumina Euro 3.1 with rich smelling exahust created by
runnig way too rich.
Exahust is black in color and has an almost in between gas/vinegar
odor. Low power seems like it is runing on two cylinders. Some more
background engine has been locked up. However, compression is still
seemingly fine acording to haynes manual 115-120 PSI on first comp
stroke. After unseizing engine it ran fine for a few months delivering
mail on a rural route (yikes!). Catalytic converter has been suspect
and eliminated.
Trouble Codes:
                      15: Colant Sensor low (Replaced)
                      23: IAT Sensor in this model (Replaced)
                      35: Idle Speed error replace IAC (Replaced)
                      43: Electronic Spark Control/Knock
Sensor(Replaced)
                      53: EGR Valve (Not Replaced but cleaned and new
                            gaskets no longer
                             Leaking)

                     Also new plugs, wires and coils.

Also two weeks ago i was cheking the ignition system control module
with test in haynes manual and all cheks out. After doing that I
cleaned up the spark pulgs again (they foul in about ten minuteswith
carbon) I hooked everything up and started it and it ran fine for two
hours thourgh various performance ranges. Next morning pull #2 Plug and

it looked cleaner than when I put it in the night before, put it back
and try to start and same problem starts again running rough and rich
exhaust. Talked to some one who works at
ford as a mechaninc and he said try the O2 sensor. I did and no change.

I have tried to eliminate as many possibilites as I can but this seems
to be and intermitant problem (our favorite kind) and like that friday
evening if the stars are all alinged (which has nothing to do with it )

she runs. Any more suggestions.

The Answer: Code 43 Knock Sensor/memcal I ended up having to change the
computer if it was just the e-prom or the brain box that it is located
in the cause is unknown i just replaced both.

Parts bought at a GM dealer at a total of $280 or so but from what i
looked up cheaper than a-zone and at least garunteed to work unlike
junk yard. My what a fun experience!