2000 Sable cylinder 4 misfire
 

code on diagnostics shows 4 cylinder misfire followed Autozone suggestion and put gumout injector cleaner only to have it do it again
changed spark plug boot , light still comes on and during acceloration
flashes ------ any suggestions?

how many miles and have you changed the plugs? Check the connectors to the coil(s) and make sure the wires to the plugs are properly seated at both ends.

106000 miles changed plugs last summer approx. 98000 miles when I changed the boot the spark plug was ok due to bad weather will check the connectors tomorrow

shouldn't need plugs. I'd pull the plug anyhow just to check and see if it's got oil or corrosion on it. That may be an indicator of a crack in the head gasket (oil or coolant leaking into the cylinder respectively). If you have a compression tester you may want to test that too and make sure that it's not failing due to bad compression. If the fuel injector cleaner worked and the car did better for a while but is acting up again, it may mean that there's some problem with that injector and at higher volume/speed it can't keep up (usually clogged in those cases but can also mean that it's failing to open properly). You might just need to use some more cleaner (run like 3 tanks straight with cleaner) and maybe try the STP (or other brand) fuel system cleaner (generally a little more kick to it than the cheaper injector cleaners).

spark plug looks ok no oil or crack on porcelein on 4 cylinder car runs ok until I put on the heater / defroster then it seems to buck up

yeah... sounds like the injector is clogged or bad. It may need to be removed to be cleaned or just replaced. do not try to do this with the engine hot or without knowing how to completely remove the fuel rails safely from the injector matrix. The possibility of fire is not so friendly.

You could try another tank or 3 of fuel system cleaner, but that will take a while to have an affect. I'd drive easy while this takes place if you opt for this route. Personally I'd take it over to a friend of mine that has some of the needed tools for fuel rail work that are currently missing from my collection and we'd have some fund under the hood on a Saturday and just replace the offending injector.