Cylinder misfire

If the coolant looks like a brownish foam you are getting engine oil in the cooling system. Probably a bad head gasket but it could be cracked head.

I am losing antifreeze- no apparent leaks. I am not losing oil.

I would change the head gasket before you lose the engine.

I had this problem on my 2002 Jeep Liberty 3.7 by flushing the head gasket sealer out as it don't have a head or a gasket problem. The PCM looks at multiple factors including ambient air temp and also, coolant temp, it stores the memory for one type or brand of coolant or junk on the sensors, so when you flush it changes, how the fuel rail responds with timing as different temps cause it to match the old PCM memory as a good temp and timing, anytime you mess with these things you must not just clear the codes, you must clear the memory then the codes and do the drive cycle relearn. The reason it takes a week is because it takes time to set the code and the computer shuts off the injector because it doesn't seem to be firing based on the old info. Clear the PCM memory and do a relearn procedure before you waste a lot of money, gas can do the same thing.