high idle when warmed up

I have an 87 supra NA and when cold the idle is normal at about 750-900 rpm however, once the temp goes up so does the idle, peaking at about 2000 rpm. When reving engine, idle drops down during decel but immediately returns to 2000 rpm. Book says dashpot however, it appears maybe not. Also thinking ISC valve or TPS switch. Any ideas ?

it could be the throttle position sensor