Hello. I have a 2010 2.3L CX7 turbo with 150k miles. and keep getting P0303 misfire. I had been noticing very rough idle and start ups prior to the code, so I went ahead and installed new spark plugs and ignition coil packs. While doing plugs, I did notice a lot of oil in position 3 so I went ahead and also did the valve gasket. I ended up having to do twice because the first gasket was faulty and I ended up having a huge oil leak afterwards.

At this point, I am still getting P0303 code so I went ahead and swapped out the spark plug and coil pack in 3 with 4 to see if maybe there was something still wrong, but no change. Side note, I no longer had an oil leak, but noticed a coolant leaked and it turned out the head of the radiator drain screw had snapped off so I had to tap it and install new one. At this point, I have done radiator flush, changed plugs, coil packs, valve gasket, cleaned MAF sensor, throttle body, installed new intake filter and reset ECU. I saw a video on youtube that explained ECU rest with 20 min idle with no AC and then with AC for 20 min, and to be honest the car does seem to have a better response and smoother idle, but I still have rough start up and keep getting the P0303 code. I

am not sure what else to do since the car seems to be running fine aside from the code and the rough idle. Gas mileage has also been pretty poor the last few months hovering around 15 mpg. I have read about the fuel injector but not sure what exactly to do. A buddy of mine is a mechanic and also suggested the fuel filter may need replacing but again, I am not sure what step to take next to get this cleared up.

Thanks for the input!

 

Forgot to mention, I also did a compression test and got 180 on all 4 cylinders.

 

Either go ahead & replace #3 injector or, if you fell like pulling the intake on & off multiple times, swap #2 & #3 fuel injectors around and see what happens.

 

Thanks, I will give it a shot. Any thought on just running a fuel injector cleaner or replacing fuel pump first as suggested ?

 

Unless fuel pressure has been tested & confirmed to be low, there is no reason to replace either low pressure or high pressure fuel pumps.

You can try fuel injection cleaner, I don't have faith in it.