OK, so I had this problem too, after reading various threads from around the web I was lead to belive varying things such as crankshaft sensor, camshaft sensor, air mass meter, throttle body or throttle control sensor.

Annoyingly after replacing the Cam sensor and Air mass sensor I find it is neither.

Just in case someone else happens upon this thread at a later date I recommend "if like me your not keen on spending money"

1. take the air mass sensor off, clean the small platinum pins very carefully, I used 2 cotton buds sticky taped together with some nail varnish remover as carb cleaner was not cleaning it properly due to not being able to get through the mesh grill properly.

2. check your air pipes ensure they are all tight and sealed, ensure there is no hissing noise, its very slight and you can barely hear it.

On the back of the throttle body there is a pipe fits to the side of it from the right hand side, inspect the pipe clean if needs be and ensure this is on properly, this was my fault that dam pipe had a very minor split in it and the car ran like a bang of hammers on tick over, yet drove fine with the odd jerk in normal driving, please do look at these things before you go spending £100 on new parts.

hope it helps someone :)

Edited by Ifitaintbroke on 09/05/2013 at 19:00