Td5 misfire then puff of smoke ?

Hi, my Td5 1999 starts and runs fine but the last few days ive noticed it seems to be misfiring (feels like a murmur if that makes sense), this happened when driving around 50-60mph, then when I press accelerator I notice it puts out blue smoke then runs fine again. I intend to change fuel filter this weekend to see if that sorts but im wondering does it sound like anything else to anyone. engine has 220K miles.

could be a sticky wastegate, or oil in the injector loom,

Injector?

as said...check for oil in the ECU red plug first...and if there is any replace the injector loom ASAP

okay thanks, as luck has it I have a new injector loom lying, I don't think it would be oil in ecu as I checked this recently, thanks for your advice will change fuel filter and injector loom tomorrow.