P0300 Code on 2009 MS3

[Number2]

Hi everyone,

I'm a proud owner of a '09 mazdaspeed 3 and I'm new to the mazdas 24/7 community. I thought I'd come here now that I'm starting to get into the aftermarket a little bit.

I have put approx. 6k miles on the car since March of this year. Last week I installed a few things to complement my CP-E cold air intake.

1.) Cobb turbo inlet pipe
2.) ETS 3.5" top mount intercooler
3.) HKS SSQ Blow-off valve
4.) str33tunit Recirc. tube.

It has been running great and I've had no problems, until yesterday I was driving home from work (1 week after install) and the CEL popped up. I had it checked out that day to find P0300 random cylinder misfire. Drove it easy that evening and filled up with gas (I was near empty)...now the cel is gone. I have continued to drive it easy for the most part, but I did get on it to see if the CEL would return, yet everything has seemed fine so far.

I have been reading up as much as I can on this code...could be a boat-load of reasons. Is my ECU learning the new hardware since I unplugged it to install the Turbo Inlet? Should I drive it until it happens again, or should I pop the factory turbo inlet and intercooler back on and see what the dealer thinks? Should I have it tuned professionally?

I'm kind of leaning towards having it tuned by a mechanic, but only if the CEL returns. Even when I had the CEL for the couple hours before I filled up my car with gas, it never sputtered or ran like poop.

On a side note, the tank of gas that I've been running on the last week, I averaged 26mpg.

Thanks!

 

[Number2]

bump

 

[Biggs]

I was just about to post about this same issue...I own a 09 MS3 its at 5200 miles as i write this. Anyway, I was driving monday night on I95 and I got a CEL outta nowhere. next day i took it to advanced auto parts and it was a P0300... now before this happened ive noticed an issue with throttle response and my shifter was very grabby and would make loud mechanical clicks and crunches when I shifted. but i thought it was something i was doing wrong and just had to live with it...

I took it to the shop yesterday (coincidentally the light went off when i started the car to drive it to the shop) So with the light now off, they ended up doing a regular diagnostics test and also called up mazda for advice. they told them to "re-flash the PCM" ...

All I have to say is holy sh!t, my car is completely different now!... Its as though i was running on only 3 cylinders before. the increase in acceleration is VERY noticable and my issues with the gearbox have gone away, the shifts are buttery smooth, and COMPLETELY SILENT! not only that, but i seem to be able to cruise at highway speed at a significantly lower RPM. I used to be doing about 3200 RPM at 70mph now its 2500. It feels like i had an AP installed.

I honestly have no idea what made this change, or why my car was acting so poorly before.. again i just bought the damn thing less than 3 months ago.

My question is is the PCM the same as the ECU? DO you think they gave me an "updated map" for my computer?

so my suggestion to you Number2 is when u take it in ask them to "reflash your PCM" its as tho i just got 30hp for free. (im not exaggerating when i say that).

 

[8.5MS3]

(rlaugh)

 

[Biggs]

(fuoops)

laugh all u want, this thing is a beast now... or should i say now i finally have the beast i should have had to begin with.

 

[Sport6]

Did you discover 6th gear? That is the only way the rpms would change at 70rpm.

It basically goes with what you are saying too:
5th @ 3200rpm = 67mph
6th @ 2500rpm = 67mph..

Not trying to be a dick but unless your clutch was slipping constantly it can't change your speeds at certain rpms.

 

[8.5MS3]

Thank you sport6. There is no way an ecu reflash will change the gear ratios on a car. Also there is no way it will change how smoothly you shift...so...yea ill keep laughing

 

[Kain]

not only that, but i seem to be able to cruise at highway speed at a significantly lower RPM. I used to be doing about 3200 RPM at 70mph now its 2500.

This must've been some magical ECU reflash to somehow have physical altered the gears in the transmission.

 

[Biggs]

i honestly think it had to do with the fact that something was screwed up with the way the engine was firing. obviously im not a mechanic so i dont know exactly whats been changed, but I am fully capable of noticing the subtle nuances of this car.

bottle line, this car is much smoother now and the throttle response noticeably better.

now im not saying i have a faster car than a normal MS3, I feel I now have a "normal" MS3... what i was driving before was not running at 100%.

now the OPer, I would suggest you going to your dealer and having them do the same thing to your car. seeing as there is nothing else really that could be done (at least thats what the guys at the shop said)

 

[Biggs]

Did you discover 6th gear? That is the only way the rpms would change at 70rpm.

It basically goes with what you are saying too:
5th @ 3200rpm = 67mph
6th @ 2500rpm = 67mph..

Not trying to be a dick but unless your clutch was slipping constantly it can't change your speeds at certain rpms.

im telling you, from the time i drove the car off the lot to the time i took it to the shop this week 6th gear was always at around 3200 rpm between 65-70. and i always felt that was a little high for that gear, It was so annoying that id find myself wishing for another gear.

 

[8.5MS3]

(braindead

 

[controlo]

(braindead

+ (bang)

 

[MikeHTally]

Mine is just a hair over 3K rpm at 80 in sixth. No tuner or ECM flash or other electronic mod can change your gear ratios. Maybe your shift knob needs to be tightened 1/2 a turn.

 

[Fazzster2]

I just went through the same thing and finally took it to the dealer. Turns out this is happening a lot and Mazda will be offering a re-flash very soon. However, they have to rule out the following: 1. bad egr 2. bad plug 3. bad plug wire 4. bad injector. If you don't get your car serviced by Mazda, you will have to prove you are using 5w30 oil by providing a service receipt.......My personal experience is that the car runs fine and the cel goes away in a day. Ironically i achieved the best milege on the tank of gas used when I had the cel. Mine comes on when I am at full boost in 5th and i let off for a second then get back on it....I have 12k miles and it is 5 months old. I got her new...

 

[jkunze]

My MS6 threw P0300 codes after changing my plugs. I eliminated the error by pulling the new plugs, checking the gap (which i should have done before installing them) re-gapping them and then reinstalling them. No more P0300s.

Edit: Plug gap should be between .024 and .028.

 

[derspi]

I've had my MS3 for about a year and a half year now and the car never threw a CEL until about a month ago. Like the OP, it ran perfectly fine even with the CEL on and after about a day, it didn't clear so I cleared it myself with the AP and it never came back. I actually got 2 codes, one was for the misfire and the second was for overboosting (I am running a custom map on my AP). At about the same time when I got that misfire CEL, I noticed that the car was hesitating a bit when going WOT in 3rd or 4th gear. Kinda like the car wouldn't respond right away to the throttle (and no, it was not lag as I've been driving this car long enough to know how that feels). So this past weekend, I pulled the Denso 1-step colder plugs to check their gap and found that they were pretty black and fouled up. They were still good if I cleaned them up and burned off some of that gunk but it made better sense to just put the stockers back on instead of having to check on them again in 8K kms. It's clear that with the amount of city driving I do (90%), the 1-step colder plugs don't get hot enough to clean themselves up. So for all you guys running colder than stock plugs and have hesitation, I'd check the plugs first.

 

[brianguild]

Guys, did they ever offer an official PCM update for this P0300 frequent cel issue? The reason I ask is that I've had this code on and off for the last 6 months and the dealership cant figure it out. New plugs, new low pressure fuel pump, all kinds of diags sent to mazda, 2 senior techs and regional reps have visited... now they are about to run a severe RX8 carbon cleaner treatment through the motor to rule out carbon buildup. Basically, they have no idea what is causing this. Any thoughts?

 

[Mid_Life_Crisis]

Guys, did they ever offer an official PCM update for this P0300 frequent cel issue? The reason I ask is that I've had this code on and off for the last 6 months and the dealership cant figure it out. New plugs, new low pressure fuel pump, all kinds of diags sent to mazda, 2 senior techs and regional reps have visited... now they are about to run a severe RX8 carbon cleaner treatment through the motor to rule out carbon buildup. Basically, they have no idea what is causing this. Any thoughts?

Mine is due to a malfunctioning EGR valve.