what were the codes?? we need them

i would start with plugs and wires/coils as they are the most common failure for miss fires

Roy

the codes were po120 po300 po304 po505 a year ago i had to do a timing belt, balance belt, and put a new head on the engine which is a 2.4 sohc at that time i put wires, cap, rotor, plugs car ran great till three months ago it started to give these codes i changed the plugs again and put a k&n air filter in when it doesn't misfire it runs good only misfires at idle if u step the idle up for a while it goes away. when it gave po304 i switch #3 and #4 injector no diffrence still misses. when it gave po300 i put injector cleaner in 2 tanks of gas didn't help.the milege went from 30 to 27 miles per gallon.did a compression check it was 180 on 3 &1 and 130 on 4&2 which is odd. doesn't overheat uses little oil . could it be something in the distributor because the coil and the advance is electronic and there part of the distributor. i don't know what to do at this point but drive it till it dies.