hello, i have a 2003 nissan altima sedan. my check engine code is P0304.

Question

I replaced the 4 coil, but in the shower still a hard start and the check engine light came back on. And when the car is at rest at a traffic light, it vibrates a little. What do you think is the problem?

Answer 1

have you check for intake leaks? have your replaced the spark plugs? you can try to swap injectors and see if the code moves over. also you have try to clean the mass air flow sensor with mass air flow sensor cleaner. I would check compression to see if you have a bad head gasket 

Compression:

Standard: 172 psi

Minimum:  144 psi

Difference between each cylinder: 14 psi

 

Fuel pressure:

At idle: Approx.  51 psi)