at about 30-40 mph, when keeping a constant speed, and sometimes when going up hill, my car starts juttering anywhere from a small barely noticeable amount, to a pretty significant amount. It happens around 1400 RPM Car is Mitsubishi Eclipse with 3.0L V6 and auto trans. I dont know if this has anything to do with it, but it started last week right after some very VERY heavy rain which I drove through and went through some very deep water [not on purpose] Right after that the temperature dropped well below freezing and the next morning the car wouldnt start for a little while. I'd turn the ignition and nothing, not a sound. After a few tries eventually I heard a whirring noise, and then another couple tries later it started up fine. I thought maybe something just froze up. Well either that day or the next, this juttering started. I thought it would go away after the temperature went above freezing but it didnt. I just had my oil changed.