I have a 1991 300SE w/110k mi. I have replaced plugs, cap, rotor and O2 sensor in the last few weeks. I have noticed this pattern. When I start the car in the morning it idles and accelerates smoothly. When the temp indicator hits 80 deg C it will have a rough idle and sputters upon acceleration. I'm thinking there is a cause and effect here. I'm targeting the rear temp sensor (4 prong) that signals the ECU. I have a feeling it's too rich when this happens. It has nice acceleration at hiway speeds, just idle and lo speed there is a stutter. Any thoughts?