Random OR Multiple Cylinder Missfire
It means you have several cylinders not running correct.
Be carefull! you can spend huge money and not fix this!
1st, Compresion test ond fresh spark plugs, check and replace Air cleaner if needed. Be aware that things like worn out camshaft lobes can cause this so if this is easy to check, do that before moving to # 2
2nd Pay a good tech with a scan tool that can see the sensors and engine run condition in real time to diagnose it.
P0300 Diagnostic Code - Random Misfire
Symptoms.
Engine may stumble or miss
Engine may be hard to start
you may notice no issues
Cause
Failing spark plugs or spark plug wires
Bad coil or coil pack
Failing oxygen sensor(s)
Bad fuel injector or more than one
Stuck exhaust valve
Bad catalytic converter
EGR valve or valve passage clogging
Bad camshaft position sensor
Bad PCM or ECM
The Fix
Best first action is a tune up, new plugs, wires, inspect all hoses and wire connections then reset the code. If it returns you will need to narrow it down to a system, coils and coil packs should be tested, catalytic converters for function ( do you smell rotten eggs?). A misfire that jumps cylinders could indicate a lean condition, do you have any other codes along with the 300? this will help clue you in to the source, check valve function to make sure they are opening and closing fully.
This is probably pone of the most difficult codes to troubleshoot, so start with the basics and work your way into the more expensive options, in many cases a good old tune up solves the problem, back it up with a fuel system cleaning and see where you stand.
Trouble code P0175 means: System too rich (Bank 2)
Trouble code P0783 means: 3-4 Shift
Trouble code P0174 means:System too lean (Bank 2)
Trouble code P0172 means:System too rich (Bank 1)
Trouble code P0260 means:Injection pump B rotor/cam intermitted
Trouble code P0404 means:Exhaust gas recirculation circuit range/performance
Trouble code P1000 means: OBD System Check Not Complete Since Last Memory Clear
Trouble code P0740 means:Torque converter clutch circuit malfunction
Trouble code P1794 means: Battery or circuit failure
Trouble code P1155 means: A/F Sensor Heater Circuit Malfunction
Trouble code P0842 means:Transmission fluid pressure sensor/switch "A" circuit low
Trouble code P1221 means: ETV MTR FB