P0300 and P0302 codes

Had a misfire code for cylinder 2 and random misfires, moved the coil to cylinder 1 to see if it would follow the coil after I cleared the CEL. It didn’t, then swapped the spark plug from cylinder 2 to cylinder 1 to see if it’ll follow the bad plug. Cleared the CEL again and it came back on shortly. It’s still saying cylinder 2 misfire.

Did some research, seems like the actuator for the runners in the intake manifold might be seized. Is this the common problem for misfire when the plugs or coil aren’t the problem?

I have an appointment with Ford Monday morning, I’m hoping they don’t just put new plugs or coils and clear the codes. Cause I know it’ll come back.

johnny.3sgte said:

Had a misfire code for cylinder 2 and random misfires, moved the coil to cylinder 1 to see if it would follow the coil after I cleared the CEL. It didn’t, then swapped the spark plug from cylinder 2 to cylinder 1 to see if it’ll follow the bad plug. Cleared the CEL again and it came back on shortly. It’s still saying cylinder 2 misfire.

Did some research, seems like the actuator for the runners in the intake manifold might be seized. Is this the common problem for misfire when the plugs or coil aren’t the problem?

I have an appointment with Ford Monday morning, I’m hoping they don’t just put new plugs or coils and clear the codes. Cause I know it’ll come back.

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Damn! Spectrum of emotions just then. Got quite excited when I read the post as this is exactly the same problem i'm having. Felt really good to not be alone in my car troubles...then immediately felt guilty for excitement at your misfortune, then felt sad for you as you're going through the same thing.

Mine came on a week ago but been too busy to look into it so plan on swapping in a new set of NGK plugs tomorrow and swapping coils like you did. Expecting the same result as you but I've got P0308 (cylinder 8), P0300 and P0316 (engine misfire detected on start up (first 1000 revolutions). Ngauge was showing high knock at low rpm driving around town too. Sent some logs to Lund and he said my WOT log from 3000-6000rpm showed no knock and looked totally normal. I'm wondering if my intake runners are stuck in the open position.

Here's a useful video: [ame]

Going to pull the manifold off as well and see if I can find any similar symptoms. A cracked runner or runner rod rattling around would explain the knock. Kind of hoping this is the issue so I/we can solve it and it's also a great excuse for a 2018 manifold

Keep you posted on what I find. Good luck.

I bought the same plugs, but didn’t wanna put them in yet, cause I wanted to test if it’s a bad plug or possibly the runners. I’m not experiencing any power loss or idling irregularities, even when I get on it. There’s no power surge.

But I spoke to the dealership already, and I can already tell they’re not gonna take my advice about checking the intake manifold after I’ve done the spark and coil test. I’ll see Monday though. I’m too lazy and figured if warranty will cover it, why not get it done lol

I’m just trying to get this resolved, so I can throw on all the stuff I just bought for the car on lol

johnny.3sgte said:

I’m not experiencing any power loss or idling irregularities, even when I get on it. There’s no power surge.

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Mine's the same. Drives and idles perfect. Since I wrote that post, i've not seen any knock at all but the CEL and codes came back. The irregularity of the knock (there sometimes, not there others) makes me think it could well be the runners. My theory is that they're stuck in one position until I hit a bump in the road or something which could jounce the runners into a different position or loosen the runner rod which then bounces around causing the knock. Hit another bump and it 'sticks' again and the knock stops.

Dealership wanted to bullshit me after I told them the spark plugs and coils weren’t the problem, they wanted to sell me on spark plugs to get to get “everything back to base” for $300 when I had a set of NGK at home waiting to be put in. I knew if I had paid for the plugs, they’d say that wasn’t the problem and try to sell me on coil packs next before even looking at the intake manifold like I had advised before hand. Keep in mind, I work in a shop and even showed up in my uniform (I had to get a rental and go straight to work after dropping off the mustang).

So I picked it up Tuesday afternoon deciding I’d do it myself, got the intake manifold off today (Wednesday) after work at the shop so didn’t have to take all my tools home — just like I thought: the runner control valve (actuator, whatever you want to call it) on bank 1 wasn’t getting enough vacuum to open the runners when they’re closed. The shaft was still intact, the runners were moving uniformly together.

Called the dealership, have an appointment tomorrow morning (Thursday). Service writer suggested I take a video and pictures to show the tech. Hopefully they’ll listen to me now.

Andrewg said:

Mine's the same. Drives and idles perfect. Since I wrote that post, i've not seen any knock at all but the CEL and codes came back. The irregularity of the knock (there sometimes, not there others) makes me think it could well be the runners. My theory is that they're stuck in one position until I hit a bump in the road or something which could jounce the runners into a different position or loosen the runner rod which then bounces around causing the knock. Hit another bump and it 'sticks' again and the knock stops.

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I think you’re right, cause I think that’s what mine are doing. My suspension is set up pretty stiff (for backroads on the weekends with friends), so the bouncing may loosen the runners when it sticks or vice versa. Cause once looking at the runner valves itself, it doesn’t take a lot of effort to move them open and close. I also got the code for misfire at startup today during lunch. Which made me want to get the intake manifold off even more after work.

For me, they would get stuck half or 1/4 of the way from full open and not get enough vacuum from the actuator to fully open them again. I’m guessing with them stuck in that position, it would give an imbalance air-to-fuel ratio in bank 1 causing the multiple misfire and in cylinders 2 and 4.

Highly suggest you pull yours off to take a look at it yourself, I had to otherwise it was going to bug me not knowing.

Resurrecting a 3 month old thread. I get the p0300 code only after a few wot runs, the car runs perfect and doesn’t exhibit any ill effects. One time a while back I got a intake runner stuck code but never got it again, so I figured it worked itself out. I have the logs at my tuner now.. i dont think its coils or plugs fuel etc..seeing as the car runs perfect and the cell only happens under wot loads..im thinking these plastic manifolds and their runners are faulty at times. If my tuner says my logs are perfect im gonna get rid of my gt-350 intake and move to a holley race intake with the runners locked out, if it even has runners. Also new fuel rails. Just took a look at my imrc’s and they not hooked up so my intake runners are locked out & wide open all the time. So that rules out any possibility of a code from stuck intake runners.. I'm switching to off road pipes Thursday and I'm thinking the high flow cats maybe on their way out will see after i look at them and then do some wot runs without cats..

Most people who are supercharged or Turbo do lockouts anyways as it can cause problems with the imrc plus there was a threat on here not too long ago where the GT350 pulled out a little bit more than the regular Holley sniper so you be better sticking up with a GT350 intake manifold unless you plan on making more than 20 lb of boost one day.

My 2015 Mustang GT with 46,000 miles has been throwing the P0308 and P0300 code for a few months now. It sounds exactly like what everyone else in this thread experienced.

Another mustang site talks about "neutral profile relearn" or crank sensor replacement (new o-ring). Apparently the relearn is one hour labor at a dealership. The crank sensor is $35 and then requires a relearn.

My experience:

https://www.mustang6g.com/forums/threads/low-rpm-misfire-p0300-or-p0308-codes-read-me.115108/

Shifting_Gears said:

My experience:

https://www.mustang6g.com/forums/threads/low-rpm-misfire-p0300-or-p0308-codes-read-me.115108/

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I may be just out of warranty on my 2015 GT. Anyone know how difficult it is to pull the 5.0 intake and check the runners to see if anything is cracked, broken, or stuck? It looks fairly straight forward, but it never is.

wjfawb0 said:

I may be just out of warranty on my 2015 GT. Anyone know how difficult it is to pull the 5.0 intake and check the runners to see if anything is cracked, broken, or stuck? It looks fairly straight forward, but it never is.

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Haven’t pulled the intake on this model but with the design of the intake it’s pretty straight forward.

Biggest thing is to take photos of all vacuum line routing and remember to bleed the fuel rail before disconnecting it or removing injectors..

I hate to necro this thread, but I just got a CEL on my '15 Mustang. The manifold is most likely the culprit, too. Given that, has anyone here had their manifold replaced? If so, did Ford install the newer manifold for the 18+ S550? I've read that you get a redline increase with that manifold. Anyways, I have to use my CarMax 90 day warranty to fix the car, but I imagine they will use a similar pipeline for the replacement part. I've printed the SSM for the issue to supply to the CarMax tech--hoping it will render a more useful service appointment.

AngelsofVerdun said:

I hate to necro this thread, but I just got a CEL on my '15 Mustang. The manifold is most likely the culprit, too. Given that, has anyone here had their manifold replaced? If so, did Ford install the newer manifold for the 18+ S550? I've read that you get a redline increase with that manifold. Anyways, I have to use my CarMax 90 day warranty to fix the car, but I imagine they will use a similar pipeline for the replacement part. I've printed the SSM for the issue to supply to the CarMax tech--hoping it will render a more useful service appointment.

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Ford replaced mine under warranty. It was a little over two years old with about 8k on the odometer.

They won’t upgrade you to a 2018 and up. It’s not a 100% direct swap and requires a tune.

I haven’t had issues with the new intake and have about 23k on it.

Shifting_Gears said:

Ford replaced mine under warranty. It was a little over two years old with about 8k on the odometer.

They won’t upgrade you to a 2018 and up. It’s not a 100% direct swap and requires a tune.

I haven’t had issues with the new intake and have about 23k on it.

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Thanks.