Rough idle, stuttering cold start, p0300

Car is currently in storage, but I believe I did take a few logs before storing it, so I’ll go grab my accessport tomorrow from the car and post what I got, if anything!

 

I'm having a similar issue as well, a sputtery idle and p0300 shows up every few days. My rpm also jumps up a bit when i shift into neutral.

What rpm does your car idle at? Mine idles just below 1000 rpms, it used to idle lower before all my mods, not sure if my tune makes it idle higher or not but everytime i disconnect the battery the car seems to struggle to re learn the idle, it'll try idling at 750 and feels like the engines about to die

 

Mine is set to idle right around 1000rpm. I was just cleaning some acorns out of my blower and decided to swap some coil packs around before taking the car out of storage, and noticed cylinder 1 coil pack has some weird residue on it. Upon further inspection, I see the spark plug hole also has some sort of crusty white powder inside of it. Not a clue what this is, anyone want to chime in? All other spark plug holes look great.

 

Crusty white powder could be residual from water. Have you cleaned your engine bay with a spray of water? Could also just be from regular use.

Ive always though it odd that Mazda never put a shield under the top mount to drain water away from the coil area.

 

Nope, never sprayed any water in the engine bay. I find it strange how it’s just cylinder 1 that’s like this.

 

I have it on my car without any issues. I cant say 100% its from moisture or water, but thats what I assumed when I noticed the same thing. Its not a consistent quantity across my plugs either.

 

Interesting. Is yours also only on the first plug well? Wondering if it has anything to do with the issues I've been having. Im going to clean the well out, and clean my coil packs, and do a leak down test as well.

 

I dont recall which ones, but more than one cylinder had it.

 

Hmm, mine is just cylinder 1, cylinder 2-4 are spotless.

 

Quick update

gave my coil packs a really good cleaning, checked plugs, cleaned MAF, and swapped my Cobb Sri filter with a new one, since mine looked to be full of mouse pee or something… and bam! Last two cold starts have been perfect, no misfire, no stuttering, just really smooth. I have no idea if this is just coincidence, but time will tell. I’ll update as the week goes on, let’s hope that somehow doing those few things cured an issue that’s plagued me for a few years now. Lol

 

Hope it sticks this time!!

 

Well, I should have known not to speak so soon! Once it got warm enough outside, the misfire came back on cold start. Seems to only happen when the outdoor temp is above 15* C or so, when the rpm’s really ramp up for an extended period of time on cold start. Didn’t happen once when it was colder outside… not sure if this is indicative of anything?

 

Try cleaning the MAF again. Then see if you can repeat the 2 weeks of happy starts. Both times you mentioned cleaning the MAF, the issue had disappeared for a bit. Do it again but dont do any other changes. Possibly get a good look at both parts of the connector as well.

 

Just cleaned it again, I’ll report back tomorrow after work, since it’ll likely be too cold in the a.m to trigger it. I’ll also toss a start up log on here.

 

It might even be difficult to get a warm day before the end of the week, lol Rain in the forecast.

 

Very old thread bump!

I totally forgot to upload any logs lol but here's a few... can't remember if any of these threw a code. I know for sure I have a log on my accessport with a start up that threw a misfire code, but my mac is giving me trouble with uploading the log, so here are some older ones. If anyone notices anything out of the ordinary, please chime in!

 

Bump...
Anyone have any input..... it would be appreciated!

 

I am a very frequent browser on this forum. I have a 08 mazda3 and I'm having this same damn problem.

I got it to stop for literally 2 months by cleaning off the negative terminal on the battery AND cleaning the 2 grounds on the drivers side of the bay. One is on the tranny and the other is right next to it, closest to the slave cylinder. After 2 months, I'm throwing the same codes except now I'm getting a p2188 code and I've literally changed everything at this point.

I've literally got nothing. I even called the dealer to see if there was any updates to the ECM and he said there was nothing. One advise he did give tho was to check the exhaust. Apparently, people come very frequently with random codes and it's all because of an exhaust leak. I'm probably gonna check that next

 

I just re-read through the thread to familiarize myself again. Did you find that only cleaning the MAF helps for a couple weeks?
Also, check what your ECT reads with your AP before and during start. Look to see if the reading coincide with the ambient temp before start up. Does the engine run smooth when the temp starts to rise. Perhaps swap out the ECT, its easy to do and you dont loose coolant. (mounted under HPFP where rad hose meets engine pipe). Dealer wants $120, Im running a NAPA unit for $35.

 

Hmm weird, ill give both of those a shot over the weekend! So frustrating.