Mustang GT misfire diagnosis

If you have had issues with your mustang misfiring only at cruising speeds where your engine is idling between 1800-2400ish. It could be your manifold. I would get engine codes only when cruising on the highway. Full throttle car felt great, drop it to 6th and let it cruise and you could feel the car missing. Swapped to a gt350 manifold and it’s fixed.

[@Foxhound302x]

I'm having the exact same issue with my car, except im getting a ported 18+ mani

[@lucafunnyguy6213]

Thank you so much bro had this same problem on my 3rd gen I replaced everything just to find out it was this 😂

[@darrionford637]

Do u know if the 2014 GT manifold has that same problem? I have p0308 code spark plugs coils and wires all came back okay also compression check came back okay it's starting to give me a headache

[@joshuavinkler7390]

The 2011-2014 share the same manifold so it is very likely. The manifold is relatively easy to remove and you can test the flaps with your hands to see if they are broken

[@joshuavinkler7390]

Another way to know if it’s this issue is if it runs fine under full throttle and gives the code under light to no throttle too. The flaps open under high rpm, if they are broken one of the flaps will remain open under little to no load and cause misfire issues