For the last month and many many kilometers, my Evo has been run hard and grannied and I *never* got the dreaded P0300 error. Until last night.

I went out and got my mechanic to change the HPI cone air intake and the GReddy Type-RS BOV back to the stock airbox and DV in the belief that with my 9.8T i wouldn't need THAT much air, and that the stock box was well capable of the needs of 23psi on the 9.8T. The stock MR DV went back in because I'd read in these forums that the stock JDM DV was good for up to 26 psi of boost.

So.

Changed out at 9 pm in the evening, and had the battery disconnected while the airbox and BOV was being changed out. Did not let the car idle much, and drove it around without problems. No CEL yet, but the car felt much less aggressive, like a neutered bull. But much quieter.

On the way back from sending a friend to the airport, I felt a light shudder. Didn't think much of it since I get this from time to time when I cruise around 3500 rpm at approximately 85 mph. When I got home, I noticed the CEL light (I don't normally notice it since my Blitz R-VIT is mounted on the dash in between the tachometer and the speedometer).

OBD-II ScanTech pulled out a P0300 Random/Multiple Cylinder Misfire Detected code, and that's where I read up more about it on EvoM. Had the code cleared last night, but on the way to the garage this morning, the CEL came up again, and this time, I distinctly caught the CEL coming on. ScanTech pulled practically the same info on the Freeze Frame, so I got the cone air filter and BOV reinstalled, thinking that it was probably due to the stock DV leaking boost at 23 psi.

CEL came on again AFTER the cone air intake and BOV were reinstalled. I forgot to get the mechanics to disconnect the battery but I did let the car idle for 5 minutes before I drove it off.

Here's where it gets interesting:

I get home, clear the code, disconnect the battery for half an hour (I can now reprogram my stereo with my eyes closed), tighten all clamps and check hoses, then reconnect the battery. Then I put the throttle to the floor and power on the ignition (no crank) and hear what I think may be the throttle body recalibrating, and after 30 seconds, I let off the throttle and turn off the ignition.

I cranked the engine to life and let it idle for 10 minutes after that, and then drove the car out, driving easy for 5 minutes, hard for 5 minutes, then cruising for another 10 minutes hovering between 3000 rpm and 4500 rpm at various throttle positions in 5th gear.

No CEL has come on so far *knock on wood*, and I'm wondering if it could have been that the airbox that was sitting in my storeroom collecting dust for the last 2 months may have somehow contaminated the MAF and tripped off the P0300 demon residing in the ECU.

In any case, so far so good. Despite spending the last 3 hours on EvoM reading the various threads on the P0300, it seems to be one of the mysteries of the Evo. If it comes up again, I'm going to try cleaning the MAF with some isopropyl alcohol to see if that helps.

What interests me here is that this problem was supposed to have been solved in the '05 models, and I have been able to almost consistently reproduce the problem by hovering between 3500 rpm and 4000 rpm in 5th gear between 80 and 90 mph.

In case anyone wonders, I'm driving a 2005 Evo VIII MR RS (EUDM) with a Jestr reflash.

Hope the info above is able to help some of you out there who have experienced this problem out of the blue. Lesson here -- if it ain't broke, don't fix it.

 

The sound you heard upon reconection of the terminals and turning the key to on was that of the ABS system

 

Would be interesting if it was, since I have no ABS. It's an RS. And yes, I have tested it (and flatspotted my tires). If you look in the fuse box, there is no fuse for the ABS, and there is no ABS unit where it usually is

 

The only relationship the air box has to the P0300 code is the airflow going through it..

If I were to "artificially" alter my airflow, I could trigger a P0300 CEL when the car would tip in lean when driving at low RPM and Slow speeds..

The only other time i'd experienced it was when I was cruising around, turns out it might have been due to my downpipe giving the tie bar a good rap when I had hit a bump at just the right speed, as it hasn't done it at all since I insulated the pipe and bar.

What I would suggest is to look for something that would alter your MAF reading, and perhaps vibration or something else that could cause the sensor to suddenly read wrong.

Another thought is your Tune or your fuel trims are off enough to require the trims or whatnot take some time to adjust, especially driving at night or when there is additional load on the engine (Alternator (driving at night with headlights on) A/C, etc..)

Take it all with a grain of salt, it may just be that the ECU was reset, and the car just had to re-adjust.

 

Thanks, Jack. Am heading out now to buy some dinner (and an excuse to drive around some more in the 16 deg C winter). Will monitor and keep you posted. Wanted to catch you online to wish you a happy new year.

Take care, and drive safe