It was a seized injector on my 200tdi engine that i had been running on **** fuel, 100miles into a 120 miles journey noticed it was down on power, head out of window and realised i was doing a red arrows impersonation!
Got to destination, engine ticking over and smoking away like a good un, cracked the injectors, no3 made no difference to the running.
Off to screwfix injector cleaner, remove and empty fuel filter, fill it full of injector cleaner, still ****, ten miles later it came back on all four and has been fine since.
Very ocassionally hesitatates to start, which is what it did before the smoking started.
Lynall