Car is running terrible, wont go past 2500rpm, no power and then limphome. Z18XE engine on 2003 car. Codes are P0301 - cyl.1 misfire detected and P0304 - cyl.4 misfire detected. Changed the plugs and substituted a known good coilpack, no change. There is a low oil level warning up but there is plenty of oil in sump. Any help would be appreciated.