Subaru ISC - 3-terminal that doesn't seem to really be 3-terminal?

[Patrick Olsen]

I'm in the "figuring out pin-outs" stage of installing a V88 in a Subaru Legacy to run an EZ30 6-cylinder (as seen here). One thing I'm trying to figure out is the AUX output(s) for the idle speed control. The ISC is mounted on top of the throttle body and has three terminals:

 

Section 9.4.2 of the V88 manual discusses how to set up a 3-terminal ISC. Section 9.4.5 specifically talks about a Subaru ISC, but that's an older style, which was mounted separate from the throttle body. That older style of ISC appears to have worked the same as desribed for other 3-terminal ISCs in Section 9.4.2 (based on both the discussion in Section 9.4.5, and old wiring diagrams for Subies that used that style ISC). The ISC I've got is wired differently, according to the EZ30 wiring diagram - the 3 terminals are:

• Power
• Ground
• ECU

That makes me wonder if it behaves like a 2-terminal ISC, but just has its own ground, so I would only have 1 AUX output feeding the ISC (as opposed to a "normal" 3-terminal ISC having both AUX1 and AUX2 wired up to it).

Has anyone seen a 3-terminal ISC, Subaru or some other brand, that doesn't operate like the 3-terminal ISC example provided in Section 9.4.2? Should I just wire it up like a 2-terminal ISC per Section 9.4.1?

 

Thanks!

[Adamw]

Correct, these work like a 2 wire valve.  Power to switched +12V.  Ground to engine ground.  Signal to ECU aux.

[Patrick Olsen]

Got it. Thanks for the quick response!