P0304 Misfire.... Low Compression Reading????

[AsianAlero]

So i had a misfire condition only at idle that i swore up and down was due to a bad or clogged injector. today i ran a compression test and it was 120psi on the bad cylinder while all the others were at 160psi. any input would be greatly appreciated. i read on an old post that someone had a rocker arm bolt which was not torqued down properly causing their miss at idle. any other ideas before i go chasing ghost?

cylinder 4 misfire only at idle. low compression at 120 psi. did a wet test and showed no change indicating rings are good.

thanks