My Contour has started alittle quirk, sometimes, after I start my car and just drive off, I come to a stop a little ways down the road and when I push in the clutch the RPM's drop to about 500 and the car fells like it is going to stall, but then it jumps back up to the normal 900-1000 range... ???????? it has only been doing this for about a month and has done it maybe 6-7 times... Any suggestions? FYI the motor has about 21K on it and the car itself has just over 57K.