87 T TOP GT302

So my Mustang is not wanting to idle correctly.
I've tried to set it to where it idle around 900-1000 rpm's and it keeps going back to 600-700. After the car gets warm the ilde will start bouncing and then it dies.
I don't drive it very much but when I do I want it to run right . Any thought would be appreciated.
I did install a new idle air control roughly 2 years ago.

88 orangepeel notch

Check for any vacuum leaks, smoke test is the best way to do this. But a good visual inspection will work for now. Don't forget about the ones under the upper intake plenum. Seems like a hassle to pull it off, but only takes 4:17 seconds to do.

If no leaks are found, check again.......

Next, pull codes to see if anything is stored, then do a "base idle reset", clean MAF sensor, then check for vacuum leaks again. I'm pushing the vacuum leak thing because our cars seem very sensitive to any extra air getting in there and messing with the AFR at idle. And seeing your car is 29 years old, I'm sure some of your vacuum lines are 29 years old also. Brittle and cracking .

Good luck