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Surging/Bucking, Cylinder 8 Misfire with P0300 and P0308 Codes

CBass2288

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Between around 1500-2500RPM, somewhere in there, usually around about 1800RPM or so, the car starts surging and bucking. It's not super violent, but definitely enough to be noticeable. Drove it about 40 miles with it doing that, and the next day drove under 10 miles and the same issue occured, with it throwing a P0300 and a P0308 code right before turning the car off after driving. Based on experience, does anyone know what this could be? I'm obviously gonna listen to my tuner and I've sent them a full log, just waiting for a response but just wanted to get an opinion based on anyone's experiences. Anything would help!
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GritzNGravy

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I think their is a lot on the forums with same codes p0300 and p0308. The codes mean the computer is seeing a random misfire(p0300) and cylinder 8 misfire(p0308). Usually it ends up being the intake manifold causing the problem. The intake manifold has the variable runner flaps that give better torque down low and power up top. I guess they break and and stick open and cause misfires. I think the only way to tell is to pull the intake manifold and look. First thing I would do is swap spark plug and coil pack from #8 cylinder to a different cylinder and make sure the misfire doesn't follow one of those simple items.
 

usgiorgi

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Exactly what GritzNGravy said, mine had the same issue. If it's under very light throttle, I'd put my money on it being the intake manifold flaps being broken. The dealership replaced mine under warranty on my 16.
 
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CBass2288

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Exactly what GritzNGravy said, mine had the same issue. If it's under very light throttle, I'd put my money on it being the intake manifold flaps being broken. The dealership replaced mine under warranty on my 16.
Yeah, It's when I'm on the throttle lightly. I'm well out of warranty due to mods and tuning though so I want to make sure it's that before I buy a new one.
 

usgiorgi

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Yeah, It's when I'm on the throttle lightly. I'm well out of warranty due to mods and tuning though so I want to make sure it's that before I buy a new one.
If you have access to Forscan, you should be able to see if the flaps are actually actuating. The tech note on my repair stated that that's what they did, drive it with the scanner connected and they saw an entire bank's flaps runner control valves not actuating.

You can also take the manifold off and see if they're broken

 

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CBass2288

CBass2288

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UPDATE

The IMRC on the driver's side was broken.
 

usgiorgi

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UPDATE

The IMRC on the driver's side was broken.
Glad you got it figured out. It was such an annoying issue when I had it, at first, I had no CEL and I thought the stuttering and surging was all in my head. Then I got the CEL and had it checked out.

Good time to get a better manifold :)
 
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CBass2288

CBass2288

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Glad you got it figured out. It was such an annoying issue when I had it, at first, I had no CEL and I thought the stuttering and surging was all in my head. Then I got the CEL and had it checked out.

Good time to get a better manifold :)
Exactly! It was frustrating. I knew something was wrong but kept thinking it might just be in my head.

Ported 18 coming!
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