1989 300e. Milage 146,000. When I start the car it idles well with a slight increase for the cold in rpms. However, once the car is put in drive the idle is only 500rpms while stopped. It is a very rough idle. A slight pressure on the gas and it idles smooth. As soon as you start to accelerate it hesitates, then goes fine for a second then hesitates again until your going about 40 mph. After 40 it cruises along fine until you stop again. As soon as the car reaches above 80 on the temp gauge it runs great for about an hour, then it hesitates only during passing acceleration. It has a complete tune up. New plugs properly gapped, new wires, cap, Would my check engine light tell me if it was ox sensor? It hasn't gone on. Any ideas? Also at 146,000 is it time for a new timing chain?