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It sounds like the car is misfiring at idle. The flashing check engine light indicates misfire. This can be caused by a bad Mass Air Flow Sensor, Crankshaft Position Sensor, and bad Oxygen Sensor.
The fact that the light is coming on indicates that the car has done a diagnostic and found a fault in the system. You need to scan the car to find out what the car has found. This scan typically costs $90 at most shops. However, if you take the car to a parts store, and simply ask them for an OBDII scan and print out they will do it free.
The print out will tell you what needs to be repaired/replaced.
answer not helpful same answer received in november 2009 from certified machinic,don't like probably answers. thank you for your time.