it could be spark plugs and HT leads need renewing. if they have been replaced the engine management system sensors need checking and only a garage ( you can trust ) can do that.
my tip...never ever ask for a full service. explain the problem your having and only have that fixed.. the word SERVICE to a garage lets them know its OK to charge daft prices for checks you can get free at most tyre / exhaust places
rob
January 2007