Alrighty so im doing like 30-35 doesnt matter what speed but the moment after i push in the clutch as im slowing down the rpms go bit down but then shoot up to 1500 rpms and hangs till i come to a complete stop then it drops to regular idling. i had replaced the idle air control throttle position sensor had a edlebrock victor jr Efi manifold along with the Sr performance throttle body 75mm my mechanic also checked for any vaccum leaks but didnt seem to find any i linked a youtube video and attached a second so u get a better picture of what im talking about after i press the clutch to slow down rpms seem to hang, also someone told me maybe the dashpot settings needs to be tweaked possibly? other than that the car seems to be running fine. but its very annoying for the rpms to be hanging like that and more so when i turn the Air condition on as well. something just seems out of sync. ull see as the speed is going down the rpms are hanging. when i do come to a stop it does idle like it should. if i put it in neutral give it gas up to 5000 rpms and let off the pedal it goes down to 1500 it hangs for a bit before it goes back to normal idling
https://www.youtube.com/watch?v=ZAJsw8cGS88
When you start modifying vehicles like that all bets are off there's no saying what the software and the computer system is reading the data gets from the throttle and how it reacts to it with all those modifications. Good check for obvious things like any type of vacuum leaks or throttle plates that are sticking with all those mods even if you brought it to me my computer's might not be able to compensate for any of those modifications and what they will do when it comes to how the engine idles
I've done this fix on a few Mustangs and it worked. You may give it a try:
https://www.stangnet.com/mustang-forums/threads/fix-your-slow-dropping-hanging-rpms.541046/
