Help. My 91 YJ 4.0 just started hesitating today for the first time when going uphill or accelerating fast. I have an XJ with over 200k miles and never had this happen. I suspect either a fuel filter or a loose or broken vacuum line. The question I have is which vacuum line should I be checking?

I visually inspected all the vacuum lines at the top of the engine and looked for loose connections. Somebody else mentioned one at the bottom of the header (?)

Any suggestions of where to start?:confused:

replace your 02 sensor