Misfiring at Idle ONLY when hot.
 

Im sure this question has been asked countless times but I have been searching and searching through the forums and found no sure answer on why this is happening. Let me give you a bit of insight on what exactly I am experiencing and see if anyone can help me. So I just bought a 2004 Mazda RX8 6-speed MT with 95,000 on the dash recently, it was driving well, owner told me he got it regularly maintained, which I think is BS now. Its been about 2 weeks since and I have done an oil change and a little bit after I noticed some vibrations when I am idling and it usually jumps from 750-900 rpm at idle. I did some research and was convinced it was a faulty ignition system so I replaced the OEM ignition coils and wires with a Bennett Built unit today and used NGK iridium spark plugs. The spark plugs that came with this car were brown and looked like they had plenty of carbon build-up on them and two of them had their positive terminals broken off of upon taking the wires off. After everything was put together I started the car and everything seemed fine up until it reached operating temperatures where the the check engine light finally came on and I pulled the code P0301 which is a misfire. I don't know what else to do, I cleaned the MAF sensor and added some seafoam to the gas tank and let it run thinking it couldve been my injectors but it was still the same, perhaps I didn't plug in my wires all the way? You could also hear something irregular from the exhaust. Im lost on what else to do, could my apex seals be on the way out? But on the other hand I am not experiencing any symptoms of low compression that people usually get like obvious loss of power when I am driving or the car struggling to start up when it is hot so I am really not sure.

Check to make sure the plug wires are connected in the right order. If that looks good the next culprit is either ignition coils or a clogged cat.

Check out this thread, it is pretty detailed.

https://www.rx8club.com/series-i-tec...t-here-222280/

I already went through that thread countless times Shaozhou but thanks anyways. I have one question though, Cayman, if one of my wires, or coils are not working don't you think that I would be getting a misfire regardless if the engine is cold or hot? I am still going to double check that I connected everything in the right order and all the way, I will let you know if it does anything.

Made sure all the wires were plugged in and where they are supposed to go, still no luck, once the car was warm it started misfiring again smh. Any other suggestions?

It may not directly be because of that but it can cause issues. I just know it runs really rich when wires are not connected properly which could cause a misfire. A bad ignition coil can also be a cause though usually it will throw a code if one is really bad.If it's not that then check the cat. Those things can also cause misfires if clogged.

The car only runs rich when its cold, as I can smell fuel which is normal. I also took out my leading plug from the front rotor housing to inspect it and it already has debris or carbon build up on it and they have been in for less than 10 miles. Is that normal? And I do not think I have an issue with the cat either, the engine does not seem to be struggling or trying to die on me. Do I maybe have some sort of carbon buildup in the front rotor that is causing it to misfire when the engine enters closed loop and starts to lean out?

Well, then I suppose it's time for a compression test! first thing to really try if it was nothing simple. If it passes compression, need to do some further investigation. I would wager it's a fuel delivery problem if compression is good.

To answer your question about plugs. Brown is a typical color. If they are really black then it is running rich.

I can do the compression test with a regular piston compression tool right? I just want a general answer on what the condition of my apex seals are without having to spend $200 for a rotary specific tester.

You can indeed. It's not accurate but will at least tell you if there is damage to your seals. Main thing is just to make sure engine is hot before testing. I'll link the vid:

[QUOTE=CaymanRotary;4900793]You can indeed. It's not accurate but will at least tell you if there is damage to your seals. Main thing is just to make sure engine is hot before testing. I'll link the vid:

[/QUOTE
Just got done doing the compression test for the front rotor, which was the only one I had time for today but it was the one that was misfiring. I followed everything in the video and the compression for each rotor face was roughly 90 psi and the whole rotor was at 6.5 BAR which is acceptable, but what do I do next?

You'll have to still test the rear rotor. You need to make sure both are still in good shape. The one you tested is low compression but not terrible. Once they go under 6 bar, rebuild is necessary I find. Your numbers should look like this:

90,90,90 + cranking speed. You should get 3 numbers plus the speed at which the starter is cranking the engine. That determines if those numbers are good or not.

90 psi at 250 rpm is not passing. 90 at 200 might be. Either way, borderline.

My rpm I calculated was nowhere near 250, more around 210 actually.

Basically good enough that compression isnt the problem in that rotor in my estimation. Yea, it's a bit below minimum spec but that wouldn't cause the issues you are having. Problem could be the rear rotor though so test that one as well when you get a chance.

Alright I am back once again. I compression tested the rear rotor and got the same results, maybe a tiny bit better. But after all that, I reset the ECU and it ran good for a 100 miles. It was not shaking as much at idle like before but the light has just come on once again. Could it be something to do with my injectors or a vacuum leak of some sort?

I'm inclined to believe it's the cat based on information provided. Did you ever take it down to inspect? Another way to check it is to kick the exhaust pipe and listen for any rattling. That's a dead giveaway theres an issue in your cat.