Idle RPM's jumping up & down
 

i've owned my Z for about 7 months now & I just recently put my cat-back exhaust on. however, even before, i had noticed that at idle, w/o ac on, the rpm
hovers just a sliver below 750 but jumps up & down & w/ ac on, it does the same but just above 750. i know nissan says operating rpm is between like 625-750 if i'm correct, but i just wasn't sure if the jumping is normal or if an idle relearn/new parts were needed. any and all help is appreciated!!

Welcome,
If your idle is surging, meaning starts low and raises up and repeats you likely have a vacuum leak somewhere. Anything changed in front of the throttle body?

Yeah I changed the MAF sensor a few months ago but I did an ECU reset & an idle relearn. My guts leading more towards vacuum leak, where would you suggest i look first?

If the hoses (ALL) coming off the intake manifold are old or powdery, replace withe correct size, it's cheap. Usually Nissan gaskets are good until you try to reuse them so I wouldn't immediately suspect an intake manifold gasket. Buy/borrow a vacuum Guage from AutoZone or O'Reilly and hook it up. The reading should be quite steady at 22 or above. If the needle move wildly with rpm changes you know there's a leak.
Gl!