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runs rough

Engine

Model: 911SC, Year:1980, Mileage:165000, Type of use:Both Street & Track
Engine Runs Rough After Hard Acceleration:I have a 1980 911SC that is a solid original car. the engine/trans has 165K original miles. I keep the car tuned up regularly including CO measurments (using the O2 sensor and a dwell meter) to make sure the all systems are performing per spec. What I am experiencing is actually quite hard to explain. When the engine is at nominal operating temperature and I accelerate hard through 2nd or third gear and let the engine return to idle, the following happens 9 times out of 10 during street driving. The idle speed will have dropped to 800-850 rpm and the engine operates with a slight roughness. It seems like the timing is off slightly. If I turn the engine off and restart it immediately, the symptoms cure them selves right away. When I track the car at PCA events, I do not seem to notice the degredation in engine smoothness, even after a 15 minute track session. I am not sure if this is an ignition or fuel distribution gremlin. I am quite perplexed and affraid I might be over analyzing the cars performance. Bottom line is that I can feel a shift in performance that I can not pin down and resolve without turning the engine off and restarting. Any ideas?

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