why do my engine run rough while driving ,but runs good while idling? also smokes if idles for more than 3 minutes

White smoke usually steam indicates a blown head gasket. check for bubbles in radiator when warm, and/or milky oil on dipstick (water present).

White smoke can also show an overfuel condition with the newer catalyst systems, from the overheating of them, and the resultant water vapor. For sure watch the coolant level, but also check fuel pressure and watch to see that it holds pressure when key is off. As for coolant, look under the oil filler cap, and wipe your finger inside the opening, looking for a whitish yellow milky slime, which point to moisture in crankcase, either leaking coolant, or too many short trips where engine doesn't get fully warmed up. If it has a check engine lamp on, get the codes pulled also.