can anyone point me in the right direction? every now and again (mainly under harder acceleration) the engine suddenly starts to misfire it seems - if it was a petrol motor i would say 2 out of 4 plugs were failing. Also now and again when starting the engine it revs irratically for a few seconds then calms down.

 

First off, I would check the engine for codes to see if it is actually miss fireing. If you dont have that option, take out your spark plugs to see if they are all gunked up. The problem may be that simple. Start with the easy things to diagnose and start eliminating possible problems.
I would not be surprised if the problem was a sensor, like MAF or an 02 sensor.

GOOD LUCK.

 

T D i... has no spark plugs lol, how does it start up if hard then glow plugs but I agree VAG to check for fault codes