A flashing MIL indicates that the ECM is detecting a misfire. It knows due to irregular information from the O2 sensor B1S1. A random misfire is exactly that - random. Because of no particular pattern the ECM cannot be more specific, hence the P0300 code. The cause could be anything.

Failing crankshaft sensor would give the same symptoms- but on all cylinders..

I checked out the coils and they're good.

Found another problem, coil packs form cylinder 2,3 and 4 have rust on them and found water in the inside ons sparkplugs 2 and 3 between sparkplugs and coils. Engine has humidity on it but cant see any on intake galery wich is mounted higher. Windashield wi per liquid sistem is in good shape and cant seem to find any humid parts to indicate that water pased through.

Should i be looking at a cracked sylinder head?

I usualy take care of my cars at home. Its cheaper.

Problem was the water vetween sparkplug and coil. Eectric discharge was going into cilinder head instead of sparkplug. Put half a liter of isopropilic alcohol in gas tank just to get rid of any water if there's any.

Problem solved. Thank you very much !