Hi all! I'm going to try and make this as simple to read with zero to little fluff to acheive an answer. I've searched around with random bits of diagnosis I've made but have not come to a solid conclusion.

2003 Evo, 73k, stock ignition, cbrd tune with bolt ons, hks 264/272

October, 2012: On the freeway cruising at 70mph in 5th. 1 cylinder shuts down and a CEL clicks on. Getting off the throttle and getting back into it seems to reset the issue for about 5 seconds then a cylinder shuts down again. I can repeat this process to get home for what I presume to be indefinitely (20 miles of doing this for sure). Also, this only occurs with enough throttle to keep a constant speed, I can go WOT and all cylinders fire beautifully. This also does NOT happen at low speeds (under 50mph). Code is p0300.

After a while, I thought this was directly related to rain getting in my engine bay through the hood and shorting out a sensor, coil, etc but many months went by of rain and snow where this did not occur below.

The issue went away for months, I even drove 450 miles straight to NJ and another 450 back with not even the slightest hiccup.

January, 2013: I start getting p0300 with the misfire occuring at 3000 rpm (same rpm where the October incidents occured) according to the scanner. I do not feel this at all and the car continues to drive like a dream.

Because this code keeps showing up (even though no hiccups), I decide to replace the plugs and clean the MAF (which was a messy wreck). Replacement plugs were BR7EIX gapped to .24. Plugs removed were the NGK ILHxxx gapped to .28, mileage on these is unknown. I reset the ECU as well.

300 miles go by, drives nice, then p0300 and back to my October issue with the cylinder shut down all the way to work this morning. Fires on 4 for about 5 seconds then cuts down to 3. Let off throttle completely and get all 4 back for about 5 seconds, back to 3, REPEAT.

~~Any ideas would be appreciated, I'm not entirely familiar with this cars electronics but the things that came to mind are listed below with why I think so in ().

-Crank trigger plate not picking up to the sensor? (no idea, just came to mind)
-Rain fouling out the cam sensor right under the hood? (hoods wide open to rain)
-Coils are beginning to go? (single cylinder shut down, assuming same cyl)
-Throttle position sensor? (only occurs at a cruising throttle)

Thanks guys and my apologies if the structure of the above is all over the place, trying to recollect everything and put it on paper. Let me know if you have any questions!!!

 

Please search P0300 you'll find tons of info.

For your situation get with a local tuner have them disable the P0300 code routine in the ECU.

Enjoy your car again

 

I have searched p0300 but I'm going to again, maybe I have overlooked others symptoms. Are they pretty similar to what I mentioned? I hate to beat a dead horse if that is the case.

Also, I have turned off similar codes on Subaru's with 1.3 cables, I assume the process is practically the same here?

Appreciate the reply!

 

First thing I search I find this, total failure on my searching abilities...


alright i hope im on the right forum thread. i have the 03 evo 8 i have been dealing with this p0300 code for a while now.. when im driving on the highway at a steady speed the car misfires like HELL, i would have to let off the throttle and accelerate again.i changed plugs coils look fine.. and i just got it tuned and still have the same problem.. there has to be someone here that has my problem and can help out with this ..

 

.... i had the same problem.... i was given the wrong plugs. replaced them and had no further issues

 

This issue dates back to 2003. Highway cruise light pops on, car stumbles, let off gas, back on, car normal.

Mitsus find, drivetrain harmonics are what causes the code to trigger. Misu's fix, 2 updated ROM images from 0008 to 0014 and 0015 worked for some not for all.

Real fix. Disable the P0300 code routine in the ECU and never worry about it again.

 

Broke valvespring will cause it to run on 3 cylinders.

 

And this would only occur when cruising at 3000 rpm and go away when the accelerator is worked?

 

As already stated...It is a pretty common issue. I disabled mine a few years ago and have not had any issues like it since.

I used to get the stumble on the highway every 10 seconds. Somedays worse than others. It would go away for a little bit when I lifted my foot off the throttle for a sec. It would always throw the P0300.