Nissan Almera engine misfire at low revs

HI, I have a Nissan Almera Tino 2.2tdi 2001 that starts and ticks over at idle fine but when you accelerate at around 1000-1500rpms it misfires badly. When you get over 1500rpms and the turbo cuts in it stops misfiring but lacks power, like you're driving with the handbrake slightly on. It has recently had a service for new glow plugs, air filter, fuel filter and the MOT emissions were low. The garage ran diagnostics which didn't show anything but they put on a new air flow meter yesterday which helped abit but not much. When the engine is cold and the car is on choke it runs fine until the engine warms up and it misfires again. It started about a month ago and is progressively getting worse.
Please help as pulling my hair out!