Recently changed the fuel pressure regulator vacuum pipe and this cured the hesitation problem i had now i have a idle problem this is only apparent with the lights on and when coming up to a junction the idle will drop to around 500rpm then raise to 900 and settle i cleaned the idle valve this morning and reset the ecu it was ok for a short while then back to droping again also the car seems to run rougher when the lights are on. will check the charge rate and drop test the battery in the morning. also when i come up to a junction to stop the idle will stay at 1000 until i stop then drops to 900 been doing that for ages lights on or off. The main issue at present is the drop off to low idle with the lights on its a mk5 1.25 zetec. air filter on top variety

 

This might sound really daft, but I had a very similar problem and it turned out out be a leak on the air induction pipe after the mass air flow sensor. Replaced the pipe, and after a couple of miles it settled down and went back to normal......