OK, here goes. 99 Forester with 2.5 SOHC. Put in new head gaskets, timing belt and everything that goes along with the job. After starting I have rough idle and po304 code. Have only 35 psi in number 4, but it will hold 125 psi during leakdown. Took timing belt off and reinstalled seemed to run better, still rough idle but no po304. runs great on highway but can hear spark knock sometimes. po170 code started showing up so i changed both o2 sensors to no avail. runs rougher than ever and po304 is back. still low compression in #4 any ideas?