You need to find the hiss because if there is a hissing vac leak. Thats probably it. Mustangs wont run right with
No codes at all. Which I don't understand cause this has been doing this for about a month nowDepending on the size of the leak, pulling in a little bit of brake cleaner may not make it stumble.
Do you have access to a vacuum gauge by chance?
Additionally, have you attempted to pull codes? At a minimum, you should be getting an O2 sensor out of range code.
I have a small suggestion on what it could be. I never heard a hissing noise, just engine noises. But I think it has something to do with the intake manifold cause there is oil sitting at the bottom of it from the pcv valve.Yes, she needs to find a vac leak, but she’s already reported it shows a misfire, and someone posted how to check the ignition components. Don’t get the owner chasing squirrels when there are two elephants to address that are not going anywhere.
I already did a vacuum leak test and couldn't find any. There is a hissing now that comes from the engine