Another P0300 Code Thread but with solution

[JIN2012]

Ok so first off I wanted to warn those of you that are still running OEM intake filters. These filters were what started the drama. What happens is over time they dont just get dirty, they also tend to warp around one of the sides.

Ok so it started off with me going to the dealer to get a heatercore coolant line replaced that burst. After they fixed it they told me I had two codes P0171 and P0300. They were blaming the cels, on the driver side catalytic converter. They were even nice enough to print out everything the consult pulled up . One of the pages showed the bad signal from the driver side catalytic converter, compared the straight line passenger side. Another page they didn't go over with me (but that I found interesting) was one that was showing the misfire counts of all the cylinders. I noticed only the passenger side cylinders (1,3,5) were misfiring a lot compared to the driver side which was only having 1 misfire in one of the cylinders. I told them I was getting the car towed back to my house cause there was no way in hell I was going to willy nilly hand them 1k+ for a catalytic converter when it doesn't make any sense as far as the codes go for that to be the cause of the codes.

After getting my car back at my garage I began inspecting the passenger side intake connections. Didn't notice anything so I pulled out the intake filter and noticed that the passenger side one was warped so bad that when you pull out the intake filter holder and hold it up to a light (with the filter on it) you can see that one side was not sealing around the holder and was letting more air in. The driverside, you could also see it was starting to do the same.I replaced with oem ones again (for the time being just will need to replace every oil change). I cleared the codes with torque app then started up the car and now the AFR looks good, the high idle was gone (forgot to mention it was having a high idle) but the p0300 code was still present. I then ran the test results function and looked for the misfire counts and sure enough the passenger side cylinders were still having a ton of misfires even though the car sounded normal. So I shut it off, realized the spark plugs probably have never been changed so I bought the original FXE-24HR-11 Denso plugs from an Autozone and installed those and now the P0300 code is fixed.

I'd say this to anyone that gets this code; If you get it, get torque app pro or any other obd2 tool that can show you cylinder misfire counts. If you see more than one misfire on a cylinder and or multiple misfire counts on more than one cylinder start by checking your intake connections including the filter for the bank pertaining to said cylinders. maybe try cleaning your maf but honestly unless you know you're running filters drenched in oil I wouldn't bother. What's causing the code to appear isn't a "catch-all" code. It's pure and simply that you have more than one cylinder misfiring so you need to start with finding out which ones and from there see if there's a thing in common that could be causing it and go from there and try to start with the most basic reasons for having misfires not with crazy theories.

[DieselKrampus]

IMHO if you're running stock airboxes, K&N/AFE or similar style reusable drop-in filters are the way to go. The rubber "frame" around the filter is much more substantial than the cheesey OEM filters and holds it's shape in the filter tray much better. Plus being able to wash and reuse them saves $$$ in the long run. Just some food for thought. Glad you got the issue fixed and didn't end up wasting $1k on a catalyst that didn't need replacing!

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[Dreadnaught]

I've always used OEM intake filter and have never have had a problem with them warping. Sounds like you're not the original owner of your Z. It sounds like maybe the previous owner(s) did something to make the filters be warped and didn't really take care of the car.