For a while now my car has had a problem where there seems to be alot less engine braking than on other cars ive had. When im driving along at say 55mph il let off the throttle and the speed will stay at 55mph for a couple seconds before slowly reducing. Now ive noticed that the problem is worse when I have the air conditioning on and when it is the revs will slightly stick in between gear changes. Also today after a long drive I stopped at some traffic lights and the car tried to stall and then the revs shot up to 1400 and then back to 750

Also the car idles quite low at just under 750rpm which picks up to about 800 with the a/c on.

So what I need to know is has anyone else had this problem, what caused it and was it expensive to fix? Cheers for any help.

The car is a 1999, 1.8 petrol Focus.