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Q: Service Engine soon light blinks/steady at times. Engine idles hard at stops on 2004 GMC Envoy

Service Engine soon light blinks/comes on intermittently. Steady most of the time but blinks briefly when accelerating. Engine seems to hesitate and idles hard at stops. Started after refueling
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A blinking check engine light signifies a serious problem a scan tool is need to retrieve codes and pending codes stored in the computer in your car. If the Check Engine Light/Service Engine Soon light illuminates while you are driving, the car's on board computer sees a fault in the engines management system that is causing an excess amount of pollutants to be emitted from your car. This could result in engine damage if left neglected. Some problems that can cause the Check Engine light to stay on may take two "drive cycles' to complete before illuminating the Check Engine Light. The computer sees a problem and looks for an identical set of circumstances to occur to confirm that it has indeed seen a problem before turning on the light. A Check Engine light that continually flashes while you are driving is serious and is a sign that the computer sees a problem that seriously risks damaging the catalytic converter which may result in an expensive repair or even may cause a fire! Diagnostic codes are stored in the vehicle's computer and can be retrieved using a scantool that communicates with the computer in your car. We have in our Repairpal website an encyclopedia with in depth articles about computer, and computer control systems, emission and driveability problems.
Thanks Patrick for your answer. Took vehicle in for repair. System was receiving a P0304 and P0128 code. Technician found #4 cylinder coal corroaded and fouled spark plug. Replaced ignition coil, all spark plugs, and thermostat. A bit expensive but, it runs now almost like new.
Bad gas will do that. Its becoming more common these days. Get you gas at the same place every time if you can and report the problem as soon as it happens.
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