Chevrolet Repair: misfire and engine dies, chevy astro, cylinder number

Question
I have a 1997 Chevy Astro 4.3L About 3 months ago had a misfire with a po300 code. I changed the sparkplugs ignition and coil wires rotor and cap. This helped and after a week engine died twice once at 35 mph and at 70mph.  There was no warning or misfire or codes set, almost feels like someone turned the key off.  On both occasions the engine started back up with no problem and drove on with no misfire or any  other problems.  I now replaced the crank position sensor and ignition module.  The engine worked OK for about 4 days and yesterday felt like it misfired a couple of times.  The engine starts right away whether it is cold or warm.  I also  noticed that when there is a misfire, it is rather harsh jerking as there is more than one cylinder acting up.  Last year I replaced the fuel pump with a GM replacement and about 6 months age changed the induction gaskets due to a water leak. I don't know where to go next and would appreciate your help.  TKS.

Answer
Ah yes the PO300 code..... whats does this mean ?

Basically this means that the the car's computer has detected that not all of the engine's cylinders are firing properly.
A P0300 OBD code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.

Symptoms

Symptoms may include:
the engine may be harder to start
the engine may stumble / stumble, and/or hesitate
other symptoms may also be present

Causes

A code P0300 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

Possible Solutions

If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
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.


Hope this help you and future people about the infamous PO300 code.