Over the past couple of weeks I've been throwing misfire codes at idle. I got a cylinder 1 misfire code once, and I've had random multiple cylinder misfire codes about five times. I first assumed it was the plug wires, because whenever I've had misfire issues in past cars replacing the plug wires has fixed it. This time new stock replacement wires didn't help.

I've done some searching, and spoke with Mitsu, and it sounds like it could either be my coils, or my front O2 sensor dying and causing the car to run really lean in closed loop. That stuff is not nearly as cheap as plug wires, so I'd really like to figure out which one it is instead of just taking a guess and swapping parts.

Some details:

• I have never thrown the code while driving, only while idling.
• I have 39,000 miles.
• I don't have a wideband yet, but I do have a Tactrix cable and can get logs if it helps.

My mods are:

• Buschur MAF pipe and filter
• Ported and coated exhaust manifold and turbine housing
• Buschur/Ebay stainless coated O2 sensor housing
• Buschur turbo-back exhaust
• Walbro 255 lph fuel pump
• Forge Unos MBC
• Evo IX metal blow-off valve
• Jestr tune

I'm leaning toward the O2 sensor, because I feel like if my coils were going I'd be throwing the code while driving. Does anyone know how I could narrow down the problem? Is there anything it could be other than coils and O2 sensor?

 

I think I may have a similar problem as you, which I've been trying to diagonse for months. Do you have any problems with 5th gear, like low power in the 0-3k rpms range?

 

I don't generally spend much time below 3000 RPM, but I haven't noticed an unusual lack of power... that is, the power below 3000 sucks because the turbo's not spooled yet, but it pretty much feels like it should, in my opinion.

 

sounds like you guys need new spark plugs... or to have them regapped..

 

I'm sorry, I should have mentioned, my plugs are new as well. I swapped out the stock plugs for NGK BPR7EIX (iridium, stock heat range) plugs at 37,500 miles. I've since pulled the plugs to see how they look and to double-check the gaps; they're fine.

 

i have the same issue but only when its cold outsdie and when coming to a stop i throw a cylinder 4 missfire code.

ive pretty much given up on since ive had many tuners tell me my cams might throw the code.

 

FYI

when changing plugs (oem) , do NOT adjust plug gap , or you may damage the material and create driveability problems.

 

my car is doin tha same thing P0300 code when idling changed plugs and still misfire if anyone can help it will be much appreciated

 

If you have a misfire at idle most likley it is from too much advanced timing in your tune. Just something you will have to live with. Get a C-reader and leave it plugged in.

 

yea i got one and clear it everytime, i was jus a lil nervous bout it, dont want it to blow up on me...lol...

 

i havbe had it twice at idle in four months.... c reader cleared it the 2nd time and it never came back, I do not leave it plugged in at all. I dont liek it im getin gwideband for xmas so i duno maybe ill find smoething out.

 

Ok ladies and gentlemen! I have the same problem! I get a P0300 at all different times when I am driving, cruising, WOT, idle, 1st thru 5th gear no matter. Idle is smooth when its cold but as soon as it hits closed loop not so great. hit or miss. I'm working on tuning with Chris at Mellon and he has helped me fix or decide on all kinds of stuff (Awesome Tuner highly recommended!!!!). Anyhow here is my list of MODS. I would love for someone to figure this out for me!!!!

ARP Head Studs, Oil Catch Can, Buschur 3” Exhaust, Buschur CEL fix, Injen Intake and upper I/C pipe, Walbro Fuel pump, Hawk Brake Pads, Rims and Tires, AMS lower I/C Pipe, HKS 264I/272E Cams, AEM Tru Time Cam gears, Zaklee Clear Cam Cover, Ebay AMS knockoff FMIC, Cusco Twin Disc Clutch, Blitz SBC i-D Boost Controller, Forge Billet Waste gate Actuator, Stainless Steel O2 Housing, Tubular Exhaust Manifold, Boost Gauge , AEM WideBand AFR Gauge, EGT Gauge, Oil Pressure Gauge, 3 Gauge Pillar Pod

THanks for anyones help!

Joshua