I'm working on my friend's 1985 300TDT (225K miles) The major complaint is that his car shakes substantially upon start-up (as if it were a cold winter start-up) and at the same time it smokes a lot too minutes after it starts up. Once he's out on the highway, it's fine. Drives well, smokes no more than any other time at highway speed. Even when the engine is warm and at idle, it still cavitates something fierce. I've done all of the maintenance on his car for the past five-years.

To summarize: it smokes a lot upon start-up with cold engine and at idle with warm engine. It vibrates a lot at start-up whether cold or warmed-up.

So far I have done: changed glow plugs (probably 20K miles ago)/ routinely changed air filter (no obstructions found anywhere-change it every 20K or sooner if necessary)/ both fuel filters every 10K miles (lately the clear in-line filter has been black with sediment, I changed it and figured he got some bad fuel, that was 20 tankfuls ago-inline filter is clear)/ran one can of Diesel Purge through system, no improvement/ adjusted valves 35K miles ago (he's 5K overdue - I doubt that's the problem, 75K overdue, maybe)/ thermostat replaced (MB brand) 18 months ago/crankcase ventilation has been checked-no obstructions found/no evidence of oil in coolant or vice-versa.

Can anyone shed some light on why this is smoking and vibrating so bad? Thanks!