Probably the mass air flow meter, although this is in the wrong section,
The MAF is in between the air filter and your injector.
Only reason I know is I had the same problem, Also recommend looking at the crank sensor also as this controls the revs/idle speed. google your problem.
look at this website its brill, helped me out when i had problems with the same car.
All the best.
Copy and paste this into your address bar.
http://www.cavweb-forums.co.uk/forumdisplay.php?f=83
daz, May 2008