Hi all;

Freaky-running engine question:

I've got an 85 240 with about 290,000 miles on it, still happily running strong, at least until yesterday, anyway. Well, at least it waiting until the day after I came back from 6 hours of highway driving.

Yesterday, started/ran perfectly fine, drove about 10 miles, shut it off for an hour or so.
Started up promptly, but felt rough at idle, relatively okay under power, sort of dead spot in-between.
Drove it home, engine rough, smelled of unburned fuel.
At home, exhaust somewhat visable (but not smoking).
Engine temp normal.
Checked wires/plugs, all functioning, black residue on plugs.
Checked hoses for vac leak, happened to find one, fixed same.
Threw on a vac guage since I had the vac hose in my hand, vacuum at idle and higher running 15psi (should be 20psi-ish) typically indicating "wrong timing" range.
Runs somewhat better with vac hose leaking than not
Checked timing, correct at 12ish but reading lurches erratically (more advanced) with engine stumble.
Timing advances normally on rev-up, but engine burbles and acts as as if one or more cylinders are missing as it revs up.
Unacountably, engine knocks slightly on shutdown.
Pulled timing belt cover (needed to check condition of belt anyway) belt/teeth in fine condition, cam timing correct.
Starts immediately every time.

Suggestions? Thanks in advance!