[SOLVED] Rough idle, stuttering cold start, p0300

Alden

Alden

Greenie N00B Member
Greenie Member
Hey guys, just got an account here, however I was a member of the mazdaspeedforums for many years. I’m looking for some help on figuring out some possible causes of my problems.

a little background, car is a 2012 speed3, basic bolt on. Full turbo back with high flow cat, Sri/tip, intercooler, hpfp, egr delete, AP with custom tune.

the car began to have a pretty rough idle during the winter, and started stumbling quite a bit during start up. This all happened shortly after my fuel lines froze one night, and I tried to get it going with no luck. Eventually she fired up after it go a bit warmer outside.

Has anyone ever had a rough idle like this? (Video below) if so, how did you fix it? The idle in the video is much worse than it is right now, I’m not sure if the cold has something to do with that?

I’ve also been having a P0300 code pop up, unrelated to this event, as it’s been happening for about two years, very rarely.

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If you’ve made it this far, thank you. Lol
 
What wheels are those? Im shopping for wheels that look exactly like yours
Now in regards to your question, I recently had a misfire on cylinder 2 (P0302) that sounded similar to your car but not as bad. Did a compression check; all cylinders except for cylinder 2 were at 160psi, cylinder 2 was at 140psi. Its at the shop getting built now.
 
Blighted said:
What wheels are those? Im shopping for wheels that look exactly like yours
Now in regards to your question, I recently had a misfire on cylinder 2 (P0302) that sounded similar to your car but not as bad. Did a compression check; all cylinders except for cylinder 2 were at 160psi, cylinder 2 was at 140psi. Its at the shop getting built now.
Click to expand...

wheels are Miro 398’s 18 x 9.5 et35.

And I just changed my spark plugs, checked compression at the same time and pretty much 180 across the board! I also cleaned my MAF. Issue seems to be resolved now, idle seems normal, cold start sounds totally normal now. Time will tell, but I also had my idle jump up and down a bit when I’d put it in neural before coming to a stop, not sure what that’s about.
 
Keeping that maf sensor clean certainly helps matters. Putting into neutral while slowing down and having a bit of a bump in rpm to me has always meant I put in neutral I little to soon. Now I could be wrong on that.
 
Awafrican said:
Keeping that maf sensor clean certainly helps matters. Putting into neutral while slowing down and having a bit of a bump in rpm to me has always meant I put in neutral I little to soon. Now I could be wrong on that.
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When I mean bump, it goes up and down like 3 times then settles. Doesn’t do it every time tho.
 
Alden said:
Never really looked tbh. Nothing high tho. It will also do it if I rev the car to like 2700 rpm while sitting in neutral.
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This is only occurring when the engine is still cold? I think the description you are looking for is "hunting".
Have you done any other work on the car besides basic bolt ons and plugs? anything with the intake manifold?
 
The_big_dill said:
This is only occurring when the engine is still cold? I think the description you are looking for is "hunting".
Have you done any other work on the car besides basic bolt ons and plugs? anything with the intake manifold?
Click to expand...
Nothing other than basic bolt ons. My idle no longer jumps around at all while in neutral, but my car still has a lot of trouble during a cold start, really sounds like it struggling to stay running. It'll still throw a misfire code during a cold start. Changing the plugs seemed to have worked for like a week or two maybe? Im completely at a loss for what the problem might be.
 
I had a similar issue. Random or specific cylinder misfires for years with no real continuing issue then came the rough cold start like yours. Then a few months ago cylinder 3 misfire became awful to the point of a flashing check engine light while limping it back home. Thought I was in for a rebuild or a valve job at the least. Ended up replacing the injectors with a used set I picked on the old forum years ago that had been cleaned by Injector RX in Texas. Changed out the crappy little stock injector seals that were definitely leaking with Corksport injector seals, the misfires and rough cold start/idle are gone. Hope this helps.
 
The_big_dill said:
Do you have logs?

Pull the spark plugs and take some pictures of the tips.
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I took a log before putting it in storage last night, I’ll post it up here after I’m done work. As for the plugs, it’ll be a while till I see the car again lol so those will have to wait.
 
Benny71 said:
I had a similar issue. Random or specific cylinder misfires for years with no real continuing issue then came the rough cold start like yours. Then a few months ago cylinder 3 misfire became awful to the point of a flashing check engine light while limping it back home. Thought I was in for a rebuild or a valve job at the least. Ended up replacing the injectors with a used set I picked on the old forum years ago that had been cleaned by Injector RX in Texas. Changed out the crappy little stock injector seals that were definitely leaking with Corksport injector seals, the misfires and rough cold start/idle are gone. Hope this helps.
Click to expand...
This is good a bad news. But, I’ll be getting a used set of injectors with some almost new CS deals which I’ll be installing in the spring, so hopefully it resolves my issue.
 
Just a little update..

I swapped my injector seals, and cleaned intake valves. Unfortunately, this didn't solve my problem, so I'm beginning to think it might one the injectors themselves. I should have sent the injectors out for flow testing and cleaning when I had them out, lesson learned. I found a guy who's willing to sell him used injectors for 80$ and they look to be in great condition, so I'm going to buy those and send them out for testing/cleaning.

Car still misfires on cold start, but sometimes If i prime it before I start it, it doesn't throw the code but still sounds all over the place until it finds idle. I will update once again after installing the other set of injectors! Lets hope this actually works... tired of spending money on finding a fix lol

I will also post of up some logs of a cold start, and an idle tomorrow sometime.
 
Hey if you don’t mind me asking did you ever find the answer to your misfires I have the same problem I have done numerous things and I cannot find the problem I would love to see what you did so maybe you could help me thank you
 
Di23783 said:
Hey if you don’t mind me asking did you ever find the answer to your misfires I have the same problem I have done numerous things and I cannot find the problem I would love to see what you did so maybe you could help me thank you
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Still haven’t figured it out! Changed injector seals, swapped fuel injectors with clean working ones, cleaned IM, changed spark plugs, issue still persists. It idles normally now, but whenever I cold start it, it sounds like I have a VTCS delete and I throw a random misfire.
I’ve just decided I’ll override the cold start every time… even though I really miss those loud cold starts! I do plan to check a few more things this summer though, once it’s out of storage. Hopefully I figure it out eventually, it’s rather annoying!
 
Alden, any chance you could post up the logs you collected? I just went through the post, I had forgot you were still having problems since you were doing the seals.
 
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