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Discussion Starter · #1 ·
So I know random misfire codes are expected with big cams, but I was hoping I had gone small enough to avoid this.

Some background info: The car needs to be inspected on the stock tune.

The car is an LS2 car and is visually compliant for CA right now, has stock air box, stock exhaust, all emissions equipment in place and functional, stock throttle body, and an MSD intake manifold (carb exempt).

It also has a 223/230 615/607 115 cam.

All my emissions readiness monitors clear except for evap, but I’ve read that can just take a super long time and also isn’t required for smog here.

The problem is every time I let it sit and idle it gets the pending PO300 random misfire code, which eventually sets the CEL (im not sure if this is purely time, or after a set number of start cycles). It will go away driving normally and not letting it sit and idle continuously for a couple of days. Does it make sense that is purely a cam thing at that size? I’m fairly certain if I raised the idle by 100 rpm the problem would go away, but that’s not allowed.

If that is just cam, are there any bandaids that might help get me through having to be idling for 15 minutes without throwing a code?
 

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Most tunes with an aftermarket cam (mine included) have the random misfire CEL turned off for the exact issue you're experiencing. Not sure how you're not going to have some sort of code either immediately pending or hard set with an aftermarket cam in the engine, and do not know of any work-around outside of luck that it won't trigger a misfire code while you're getting inspected.
 

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Discussion Starter · #3 ·
Bummer… They can’t fail you for a pending code technically, so I have that going for me. Guess I need to determine how long it takes to fully set.
 

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A cam doesn't need to be that big. if it has enough overlap to thump a little, the ECM will probably detect a misfire somewhere. I think the misfire tables in the stock tune are a little less sensitive at idle, and more sensitive in the ranges where the stock engine generally runs smoother and sees most of it's time, so you generally see cam "misfires" in the mid-low teens up into the twenties RPM x 100-wise.
 

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Discussion Starter · #5 ·
Thanks for the info, I wouldn’t have thought that was the case. Engine feels very smooth right off idle and normally I can feel any inconsistencies through the Whiteline motor mounts but it could just be that it exceeds the resonant frequency above idle.
 

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Discussion Starter · #6 ·
Update on this, there is a CA legal handheld tuner that has idle speed adjustment. Using that to raise my idle rpm has eliminated the code.
 
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