Plastic for cooling sucks.

What year SC400, with how many miles on it?
92 with 203K I know what your gonna say, "it lasted 200K miles.." yes...it DID. multiple cracks noted in remains. After I replaced it (2 nuts) The $160 IAC motor seized up and the idle went 1100-2100,1100-2100 like the second hand on a watch. Not serviceable: HA! Took the thing apart, cleaned the pintle, found a skateboard bearing seized up barely rotating in the housing. Kroiled it, unseized it and lubed it up good. Now it spins like a skateboard wheel and the IAC works like new. If everyone knew this trick Rock would not be out of stock! GMC Suburban had same aluminum impregnated nylon stat housings fall apart.