Locating source is ideal otherwise it's often a change everything game until it goes.
Sometimes we can trace it by a few checks eg.. If misfiring at idle.. Removing one lead at a time.. ( replacing of course before doing next lead to plugs) ..when no effect such as worse misfire or stalling occurs we have our cylinder pinpointed. Then it's often plug or lead causing it.
If we get more misfiring under load? It's often coil breaking down .
Otherwise a scan can often help identify root cause. Here also professional machines can test and check every part of a cars circuits and nearly always ( operator skills count) determine exact reason .
hornchurchmale has the best answer with the limited information. His question about when it is felt (if not just a code with no more info) is really crucial.
I would add that it very much depends on whether it is a consistent cylinder or two, or if it includes multiple cylinders and especially P0300. (if it is pre-1996, never mind.) P0300 usually (but not always) suggests a problem with the intake mixture, including EGR leakage.
First find the cause. As others have said; coil or coil pack, wire(s), plugs, vacuum leak, bad injector, stuck egr, valve clearance, timing chain or phasor issues.
First thing to do is determine what's causing it , a plug ? a plug wire ? the distributor ? a fuel injector ?
Then replace the bad part .
Here is an old trick: When its dark outside or inside the garage, start the engine, lift the hood, and spray (from a bottle) a lite mist over the wires. Look for bad sparks. It will show up in the dark.
You figure out what is the cause of the misfire & repair it
Reload, aim and fire again.
How do you fix a misfrie
