Hope someone can help, my suv check engine light is blinking then pauses and starts blinking again, idle is rough and when put in drive it shakes and runs rough, runs smooth once up to 45-55 mph, also only getting 9.5 mpg on backroads compared to 16 mpg a week ago, this just started happening within the past week, anything I can check before taking it in for service? can it be cat/convert, how much to replace or a sensor, any help or suggestions would be greatly appreciated, thank you.

 

From what you describe, it sounds like you have an overfuel condition somewhere.
When the check engine lite is flashing it is to tell you too much fuel is getting into a, / or more than one, combustion chamber and the engine cannot burn it all and therefore your converter is working overtime trying to clean up the exhaust. The c/e lite flashes to get your attention because that condition can wipe out the converter via overheating it !
There are several things that can cause the problem some are, faulty fuel pressure regulator, injector problem, oxygen sensor(s) , plugged air filter and others I cannot think of at the moment. If you were able to get the code(s) from the ECM that might help to direct someone to the possible cause.