Hi there when my car is idle iv got a slight judder and when I try to get my revs upto say 1500 and try to hold it there the revs go down but my foot hasnt moved also when I put my air con its even worse my fan comes on and when I rev upto 1500 the fan goes off but my revs drop up and down...

Hope iv explained this well enough as its really hard to explain any pointers wwould be much appreciated as im really stumped on what it could be...