im not very familiar with the 3.1 multi port, but i can tell you that my 3.1 sfi threw an iac code when my throttle body gasket was bad, basically its sucking air from somewhere other than through the filter. i would replace tb gasket. upper intake gasket, clean out egr inlet in upper intake with a wire brush while its off "mine was clogged completely with carbon" and make sure all your intake tubing is good and snug. then make sure all your vacuum is correct. if you need torque specs or vacuum diagrams or anything like that let me know and i can have them for you on tuesday when i have access to ondemand5 and alldata at school. i would definitely do this myself cuz im sure that a mechanic would charge a pretty penny for this job when you can do it yourself in about an hour for the price of 2 gaskets.
