P1399 is a pending code for random or multiple cylinder misfires.
P0300 is caused by a detection of random cylinder misfires. Start by checking/replacing the distributor cap, considering ignition tend to be the most likely and easily resolved problem causing this.
Engine misfires. P0300 corresponds to misfires that are random among all cylinders, whereas P0301-P0306 correspond to specific cylinders. I'm not an expert, but other posts I have read seem to suggest that because you are getting misfires across more than one cylinder, it's probably something like your ignition coil, distributor, etc. !
check your plug wires, and test the fuel pressure
You have to find out what is causing random misfires in the engine. See related question below.
P0422 talks about catalyst efficiency. P0300 is random multiple misfires. http://www.troublecodes.net/OBD2/Pcodes.shtml
No other code? Just "random multiple misfires"? That's odd. There should be some additional code along with the one you describe.
P0300 is for random engine misfire p0301 and p0305 are misfires on cylinders # 1 and #5 www.lextechautomotivellc.com
Maybe (it's only my random idea), maybe you should read books.
Pressure when they collide.