Thanks for the precise description.
Your problem is probably an incorrect setting of the throttle: it's too opened. Or there is a leak in the intake plenum. In fact your idle RPM is not regulated, it just by accident sets about where it should be. Actually the v8 should idle very low, 850 rpm I think, may be 800.
Do you have the Otto or EVO version ? I'm not sure intake plenums are the same of both. On Otto the plenum did not have gasket on the back side. But if EVO had about the same plenum as 3200 then there could be a gasket, it's known to leak on 3200.
There are also gaskets between the plenum and the heads, many times they are incorrectly installed.
Note that the engines sucks a huge amount of air, so it should be an important leak that you'd hear, a slightly leaking o-ring won't be enough.
The other option: on the throttle body there should be a screw to adjust its minimal opening. On a new car this screw is plumbed. But many (most of ?) mechanics (given their fantastic level of incompetence) play with this screw in hope to resolve problems they don't understand.
Find this screw and see if you can close the throttle more. You should check however that throttle does not stick when it's closed, the danger is that if it does and you release gas pedal in high rpm the throttle could be definitely closed by the depression.
Also it'd be better to slightly release the screws of the throttle position sensor before touching the screw, and then fix it again once throttle adjusted. But I'm not sure about this part, I had an automatic v8 and this part is different on this version. It's not dramatic unless you change a lot the closed position.
You can start with a test: remove the intake hoses from the throttles. Start the engine, it'll be very noisy, don't panic. let it warm up until the low idle is reached. Then progressively close both throttles with your hands. Beware it sticks. If the engine dies when you totally close the throttles then gaskets should be OK and it's probably the throttle openning. If it does not die or it's managing to run then you have a leak.