I've had the P0308 and P0300 (#8 misfire and multiple random misfires) for about a year now on my 2015 GT with about 48,000 miles. I pulled my intake off and found the driver's side IMRC shaft was broken (5,6,7,8 cylinders). My mustang isn't a daily driver, and the codes were clearing up on their own until last week. The idle was rougher, and the highway fuel economy was down from 26 to about 22 mpg. A new intake is on order. I ordered online from a Ford dealer for around $320. I hear you can get it cheaper if you know the right people on forums.
I first thought I might have the crank position sensor issue, because the car didn't seem to be driving poorly. After the codes stayed on last week I decided to search the forums again, and went ahead and removed the intake.
Video showing the broken driver's side IMRC shaft (it's metal and not plastic as I say in the video):
Picture of the broken shaft:
I first thought I might have the crank position sensor issue, because the car didn't seem to be driving poorly. After the codes stayed on last week I decided to search the forums again, and went ahead and removed the intake.
Video showing the broken driver's side IMRC shaft (it's metal and not plastic as I say in the video):
Picture of the broken shaft: