what is causing my engine to start hard and run rough? Some times it runs great. on 1992 Mitsubishi Expo

it is an intermittent problem sometimes after setting for 2-3 days it will give us the problem. sometimes after driving until its hot then letting it set for 1/2 hr to an hour time doesn't really matter. Cold and hot temps seem to cause it to react.

Asked by for the 1992 Mitsubishi Expo