2001 ford taurus engine light flashing with car shaking & dying when idles

This is my 3rd year of owning this car. Every year I had radiator flushed with heater core. This used to be a state vehicle. It doesn’t work anymore, having 2 small kids I need my heat working. The coil cost $200 & heater core is $500.I’m driving this car till it dies or I can find a job. Minnesota winter hasn’t been good to cars up here.