I have P0300 on Evo IX after HKS 272 intake cam install. I had exhaust cam for a while in the car and after intake was added my car is misfiring badly. That usually happens when I'm in part throttle or cruising on the highway at 75-80 mph. It also happens when the car is cold. The way it happens all the sudden car starting to feel like it runs on 3 cylinders and I have to take my foot off from the gas and put it back on again. Its very annoying. My mods are:

Intake
3" exhaust
S256 turbo
Full Race Iron cast manifold
38mm wastegate
HKS 272/272
880 injectors
Perrin stealth intercooler
Lower and upper IC piping
255lph Walbro

I've tried to change some stuff on my car to see if it help:
New set of one step colder iridium spark plugs
Set of different ignition coils and wires (they are for sale now)

Any help would be appriciated. I've tried to search forums but majority of posts about EVO VIII p300 and the cause for IX maybe something different

 

You should try logging your car. It might help you determine what's going on.

 

Seems this is fairly common when going to aftermarket cams. I was getting this too when I installed my FP4R cams; my solution was to advance timing on my hi/lo octane maps from 5* to 7* during RPM 0-1000 and load 0-40. Since I made that change I haven't gotten the code. I also advanced MIVEC from 0 to 4.8 in the same range.

 

yea im having the same problem... trying to work it out...there are a few fixes..

 

Lets keep solutions coming. We can make a good sticky if everybody will put their solution that helped them fix it

 

Did you have actual misfire occurring or you had a false code?

 

I send my logs to my tuner and he sent couple of solution, but nothing seem to work. Car seems to be fine until it starts to misfire.

 

sounds like your going through exactly what i did...or well still am.. no light for 40 miles.. soo we'll see but....

 

^ So it hasnt come back. Was this after trying the lower idle timing. Did you smooth more of that timing map

 

ehhh i did a couple things... to hold me over. till this weekend. which i will be putting the other parts i have on the car....


but yea trying smoothing your timing... make sure you didnt put you cam angle sensors in backwards...also check your plugs.


stock clutch?

 

No I'm on ACT street, but looking to upgrade it to Twin or Triple plate.

 

if you can, try an f-con vpro and take it to a good tuner

 

Yes I can try to spend an extra $1300 on something that might fix it and might not. I'm pretty sure that is a good system but My setup is not there yet...

 

i honestly dont think its a mechanical problem... only because now mine only pops on when my car is idling on an incline.

 

We will see if its mechanical or not, I had spoken with the guy who might fix the issue. I will have an update tonight.