What year is your rig? Add the details to you signature via My Home. A bad IAC can cause surging. Easy to check it. Need an FSM for the specs and which of the "coil" terminals on the IAC need to be metered to test. Try the link in my sig for an FSM for yours.

400HP Galant VR-4? Sounds very cool. How'd you do that- turbo I'd guess? What motor, was it the 2.4?

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Big Truck: 00, 3.5, Endeavor, 5-Spd drive line in hand!
Little Truck: 87, 2.6T I/C, MT, LSDs, Tonneau Top
Her Truck: 03, 3.8, 20th Anniv, 65k
Daughter's: 06 Eclipse, Keeping it Mitsu!
FSMs: MitsubishiLinks.com