if its EFI, then its also possible that the particular injector isnt firing. Also check the distributor cap if theres a terminal in the cap thats broken, also check the resistance of the plug wire. Def, replace the plug (might wanna replace them all while you're at it).
and while you're at it a compression check wouldnt be bad either.
and while you're at it a compression check wouldnt be bad either.