98 grand cherokee, all cylinders are misfiring and there is a random misfire i have changed plugs wires cap and rotor and ran a good fuel addtive. what else could be throwing misfire codes

Try checking fuel injector.
Try checking compression.
Is the engine running ok, maybe you're getting a bad code, if so you need to find out how to clear it, sorry I can't help you with that. Good luck

po300 is a random misfire, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why. If it was a po302 this means its #2 cylinder thats misfiring,ETC, But po300 could be any one of the cylinders. check plugs, wires, fuel injectors, Etc. Good-Day!

misfires are more from problem injectors, low fuel pressure or injector wiring than from plugs
have a fuel pressure test done to check for problem pressure regulator , problem fuel pump , blocked m/dirty filter
one other area of concern is the EVAP system where the purge valve doesn't vent the tank properly and causes low fuel flow rates

po 300 is random/ multible cylinder misfire detected po507 idle system rpm high-- go to this site for the po507 meaning--www.obd-codes.com/p507 === please go to this site for the po300 code---- www.obd-codes.com/p0300

Random/Multiple Cylinder Misfire Detected have a good day !!

301 & 306 are cylinder #1 and #6 misfire. Your spark plug wires are not in the proper firing order in relation to the correct cylinder and distributor locations.

If you already replaced the wires, I would suggest replacing the plugs, distributor cap and rotor. They are also very important parts of the spark. Fuel injector problems can also cause misfires.

I'd have fuel pressure checked, and at the very least, replace fuel filter. Not unusual to get multiple misfire codes due to low fuel pressure, thus starving cylinder(s), and causing the misfire code(s).

A code “multiple misfire” may mean that one or more of the following has happened:

•Faulty spark plugs or wires
•Faulty coil (pack)
•Faulty oxygen sensor(s)
•Faulty fuel injector(s)
•Burned exhaust valve
•Faulty catalytic converter(s)
•Stuck/blocked EGR valve / passages
•Faulty camshaft position sensor
•Defective computer

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.

remove valve cover and check valve movement

if all valves have full motion then you have a bad set of rings

do a compression test on cylinder 5 & 6 you could have intake leak.and a leaking head gasket or worn valves in those cylinders.