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engine misfire

Engine

Vehicle Information: Year: 1989; Engine (Size, Modifications): 3.3 stock; Total Mileage: 14,500;

I have had this 1989 930 for 2 years, and it has been perfect until recently. In the past 3-4 weeks, I have had the following misfire problem occur on 3 separate occasions. When I start the engine, I immediately notice the engine is rough; as I drive the tach will swing wildly, the engine acts as if it's cutting back and forth between 3 and 6 cylinders. At a steady speed (mph) the tach will read 2X the expeceted rpm when running rough, then will drop to normal reading as engine smooths. The engine continues to cut back and forth between rough and smooth. I drive home, turn off the engine, restart, and it runs perfectly! Will run perfectly 3-4 times, then repeat the above. This is through several tanks of fuel.Electronic ignition going bad? Coil? DME? Ideas?Thanks. Bob

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