having trouble with my citreon xsara,keeps loosing power?

my citreon xsara 1.4,01 plate keeps loosing power,it happens when im pulling off in 1st gear,i have to sometimes give it more gas,but its mostly when im in 2nd gear,esp when im turning into a new road,it seems sluggish and seems to hesitate for a few seconds,till i put more revs on or it will cut out,iv had a few people look at it for me,but there at a complete loss as it doesnt happen all the time,its def getting worse though,
so any suggestions would be gratefull
thank you