83 4000S sput of mostly idlingters, stalls, and sucks air. What give?

["Douglas F Davis, Ph.D." <dougster@zianet.com>]

My 1983 4000S non-quattro five-speed ran like a top until it started bucking
like a horse a month ago. It would drive fine while cold for about ten miles
or so, then it would start to cut out, buck, and lose power under load. If I
went easy on the accelerator while driving, I could get around.  If I kept
the revs up at a stoplight, I could take off without jerking or stalling. A
couple times when it started acting up during accelerations from about 40
mph or so, I floored it just to see what it would do. Both times it bucked
and sputtered to the point where no amount of gas pedal feathering would get
it back on track. It drove like it was running out of gas, then died. Then,
it started right up. I have replaced the plugs, plug wires, distributor cap,
rotor, fuel pump, and both fuel filters. Yesterday, it started right up,
would idle fine for 15 or 20 seconds, then die. If I gave it gas while
idling, it sounded like it was sucking air. Twice after it stalled, I could
hear a once-per-second clucking sound in or very near to the metering
device. I didn't notice this before. Today, it ran longer, but the oil
pressure light flickered at all rpms.  After four or five minutes of mostly
idling, it began to emit light blue smoke.  Not thick smoke, but it had
enough of an oil-type odor that I shut it off.  This has me stumped.  What
is going on?

Doug Davis

1983 4000S, five speed
1981 4000S, automatic