[$$$LEO$$$]

Can any one help my 1.6 desiel 05 plate 407 saloon has recently started mis-firing. When the enginge is on but stationary, the car kind of revs it self, first I thought I was imagining it but it is visible on the revometer. Also when driving paticulary in 2nd and 3rd gear you can phsically feel the car mis-firing. Has anybody else had this problem, Does any body no what it is, Is it any thing to worry about, Does it cost alot to fix??????????????????..

Any advice really apreiceated..........