TBI Connversion wiring and diagrams! - GearHead EFI TBI Wiring Harness Conversion ! First you need to go to junk yard and pull the engine EFI harness or complete system if you can. There will be a lot of extra things, don't worry about them now grab it all as whole as you can.TBI Conversion · Chip Programming · Tuning TPS and IAC - gmtuners The GM IAC has a pintle that extends or retracts into or out of an idle (bypass) air passage in a throttle body or intake manifold attached to the engine. Typically as the IAC’s pintle extends, air flow to the engine is restricted as the air passage is shut off.[PDF] Initial Calibration of the TBI - gmcmidwestclassics operation, the IAC pintle could bottom out on the air passage seat of the TBI, and damage will occur to the stepper motor of the IAC control. The “target idle speed” is set in a table on the chip.