Hello, as hard as it may be to believe, flushing your cooling system or heater core has absolutely no bearing on the check engine light flashing. The check engine light flashing is due to an engine performance concern that causes cylinder misfire of the engine. Where are the engine cylinders do not fire as expected. A monitor shows this to the engine's processor, which then flashes the check engine light. This kind of warning is to get your attention, because continue driving like this will cause damage to the catalytic converter and other important components within the engine. Hands-on testing is required to figure out what is going on. It could be spark plug or coil related. But that's just a guess. It also could be based engine concern related. Do not continue to drive the vehicle if the check engine light flashes and a misfire is occurring.
My next question would be: why did you feel like you need to flush the heater core? What else is going on here?
Hello, your engine performance concern and your signal concern are two separate issues. The signal concern is likely due to one or more lightbulbs burned out in your turn signal system. Or, you could have a problem with the wrong bulbs are being used. Or somebody may have tried to convert the bulbs in to some other style. Refer to making sure you have the proper original equipment bulbs in the proper spaces. This should solve your fast flashing concern.
Your engine surging issue sounds like a performance issue either with air, fuel, ignition spark elements, or even perhaps engine electric reference voltage concerns. Hands-on testing is required to figure out what is going on here. No gas available, got to test it.
Use this link to find some shops near you that can help with your concern:
www.repairpal.com/repair-shops
Sorry, your answer contained part of an answer to another question - please omit the part about the turn signals and surging. :) But do get some help from local shops as needed.