Inherited a 99

Hey folks, figured you guys would be a good start for an issue im having.

About 3 years ago I was on the hunt for a V6 mustang with a 5 speed for my dad. He loves these cars and his 3rd (at the time) was dying. I found this 1999 here in Utah about 3 years ago with 18k miles on it. I knew it'd be the last car he ever needed and scooped it up.

Well he recently passed, and I've got the car. Still mostly in good shape minus some body damage im going to fix, but I've noticed it's had a pretty rough idle. I ran a few tanks of fuel through it, and it hasn't improved. The car is now at about 31k miles, so im trying to ignore things I would normally go to for older higher mileage cars like carbon loaded egr, but wondering if anyone had any clues on places I should look for a potential age related vacuum leak?

Theres no check engine light but even with the a/c off it has a noticeable stumble/stutter at idle. On the open road she runs great, gets about 26 hwy and purrs like a kitten.

If anyone has any tips, id appreciate them!