Yeah, it would be a good idea to do both-- the IAC is the first suspect-- they do gum up badly and respond well to cleaning. Yours should have -516 that you can power up by supplying 12V to the two pins. Don't get throttle body cleaner in the motor end. If you can't fix it, they are also found in SAAB 9000 16V cars, which often have fewer miles when they hit the yards...

The linkage/TPS adjustment is probably next on the list. I went through it with my '92 945-- still didn't fix the problem, so I swapped the whole throttle body, linkage and switch from another car and it fixed things up. It looks like the throttle body butterfly shaft bushing had ovalled out on the spring end and it was hanging up on return to idle so that the switch wasn't being tripped to tell the computer it was at idle.

Aleekat's suggestions about looking for air leaks in the turbo hoses is a good one-- BTDT.

Good luck!
--
Herb Goltz, Aurora, Ontario, Canada '92 245 w/124K mi, '92 945T w/200K mi