missing out

1987 MB 190E. When you start out with it it goes ok for about three blocks. If you happen to hit a red light it sets there and goes real rich at this point and shakes and idles rough. It will keep up the miss firing and rich running for quite a ways and then it will smooth out. This happens from a cool down restart. Can you possible tell me where to look for this problem. Can it possibly be a pressure control valve causing the problem or the oxogen sensor? Any help would be appreciated. Thanks