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audi a4 1.8t quattro ...my engine check light came on flashing and the car run really rough and engine shaking like 1 of the cylinder is misfiring,,,the strange part is sometime it stays on steady and

audi a4 1.8t quattro ...my engine check light came on flashing and the car run really rough like 1 of the cylinder is misfiring,,,the strange part is sometime it stays on steady and the car runs fine.