I don't. The only thing I can think of is that mine (the earlier style) has an externally mounted IACV that has its own vac line going from inside the bore of the TB on the front side of the throttle plate to the IACV then to the Intake plenum. The later 1st gen models 88/89 have an IACV that is integral to the TB housing and don't have the vac line I have. So maybe that 4th one on top on the later style TB has something to do with the different style IACV? If yours has the 4th one I'd say trace it back and see what else it hooks to. I'd be interested to find out. I can ask around. I have a couple really knowledgeable friends.
@natalied989 thanks I have an 86 4runner only has 3 also. When I see 4 it trips me out I'm like hold up. But again learned something new thank you very much
