Bounceing Idle

got a issue on my 2001 mustang gt 4.6 2v that started back a couple months ago, been trying to figure it out, here's what ive done so far , replaced maf, iac oxygen sensors ,coils, and new accell injectors, fixed a vacuum leak on egr valve gasket yesterday but still have the issue , when i get in car after it sets for more than a hour and crank it up idles fine other that the rpms tend to hang a bit seems like , but anyway when i go to put the car in reverse and pull out of yard the rpms start to bounce way up to like 1500 then down to like 500 ,if i dont get on the gas pretty quick it stalls, but after i get on gas all is well till i park it again

tested tps and checked out but 1 thing that i seen was my tps voltage was at 1.12 closed position and i think it should be either 1.00 or lower like maybe 0.98