I recently started getting the misfire code P0304. I cleared the code and drove a day and it came back with the VSC light and running rough. The car actually would hesitate to start when this was happening like the starter was hanging up and run rough, no power. I changed spark plugs with the Denso plugs, cleared codes and it ran fine for a day and the same thing. Does anyone have any information on what to do next? I've even changed the coil pack on cylinder 4 thinking that was it. Same deal! Car only has 149,000 miles on it and runs great when i reset the code! Help! I'm hours from a Lexus dealer.

 

Could be head gasket if it misfires when cold. Maybe a clogged fuel injector..

 

why would that engine run great and normal when i clear the codes if the head gasket is bad? It doesn't make sense to me? Any way to test this? I get no other codes other than the misfire and the starter hangs up when it happens. I clear it all out and it's fine - can crank back to back no issues.

 

If by chance it is the head gasket it might be a small crack in it, after the engine warms up it'll run fine after you clear the code because the cylinder head and block warm up and basically compensate for the crack because aluminum expands with heat. When it cools down it'll contract a bit. When it expands it essentially fills the crack in. You could do a leak down test for each cylinder, but it is kind of a pain for a V6.

 

In the morning before you start the car for the first time, clear the code and drive it. See how long it'll take for the code to come back.

 

@Lexuscoast check the wiring harness (ignition and injection), leaks in the PVC hose or faulty injector (switch injectors between pistons)

 

so c0304 is your #4 cylinder. Make your you have changed the right cylinder. Look up Lexus v6 engine chart. Because number #4 is the driver side and middle cylinder. You'll have to remove your intake manifold to get to it, which is a pain in the ***.

so I recently had multiple misfires and after changing sparks, coil and boots. I even changed my intake manifold gasket because it was already off. I found out I had a vaccuum leak which caused the misfire. Even though the code said it had only misfire codes, that may not be the only reason.

 

Could be a clogged or bad injector, Vacuum leak, dirty throttle body, wiring problem in coil harness, or a compression problem in that cylinder.

These are the things you can do.

Remove injector and clean it. See youtube for a procedure.

Check wiring harness while vehicle is running poorly (wiggle it around to see if it helps).

Do a compression test on cylinder 4

Check for vacuum leak (see youtube for procedure).