Could be a few different things. Spark Plug, plug wire, coil, injector, ignition module (these are most common) Head gasket, cracked intake, mechanical (ie valve,piston,cam etc) (less common)
Check your spark plug connections and spark plugs. If necessary, replace them.
P0303 : misfire cylinder #3
Was an intake manifold gasket for me.
Cylinder #1 misfire.
Auto Zone will check your computer codes for FREE...
In the past I have had an engine misfire due to a bad fuel injector. hope this helps.
Could be a bad ignition coil each cylinder has its own
po301 means cylinder 1 misfire
my 2002 alero is missing and has no power what could b wrong
on the right side of the engine block.
code p0302 is cylinder no.2 misfire detected
p0308 is a cylinder 8 misfire , can be several reasons why