Tell me what you know about them. Pros and cons of blocking off. Thanks

Computer controlled vehicles rely on idle air control to set idle RPM. You're throttle valve adjustment screw sets Base RPM, which is significantly less than idle rpm - generally (I have the ford procedures, but not sure on Mitsu - if you haven't touched the idle screw, leave it as is). Your computer uses the IAC/FIAV to change your vehicles current RPM to what it has set as desired idle RPM. Once you start opening the throttle it's unused.

Unless you're going with a DSM link, I'd recommend against blocking off, as your comp expects it to be there, and if it's not functioning will probably go into a failsafe mode of some sort. Even with a DSM Link, personally I'd still keep it, as you can tune it's behavior at that point.

Honestly I can't think of any Pros right off of blocking/removing it, other than it being one less electronic part that can fail. Likelihood of failure is low (might need cleaned at most).

Guess I should've read into it a little more first.

It seems like the MITSU one has 2 valves, one electronic, one based on coolant temp. I could see reason for blocking off the coolant valve side of things, however due to the nature of the valve, it's open until coolant gets hot, so if you block off coolant then it will always stay open. As a result, you'd need tuner capability to tell the electric valve to stay more closed. On Fords the whole process is handled electronically.

Though You could do a partial block off, again I'd probably just leave it alone, unless for some reason you want to get it to idle more slowly when cold, or more consistently across the engine temp range.

I have had very little good luck with any of mitsubishi's FAIV/ISC's on any vehicle. Every one has idle surged leading me to block off the entire computer's control. If your ISC/FAIV are working and you are happy with your idle, then leave them alone. If they stop working, then block it off.

I could see the 2 part control causing issues, with the coolant driven and electronic driven. Idle surge is usually from the computer overcompensating for some other issue. While you can fix the surge by bypassing, you may have other issues that need addressed.

Not trying to contradict NCGalant by any means, he's way more of an expert than I am, and I don't know the inner workings on DSMs, so don't know if it'd have any major effect. Obviously if you have no means of tracking down what causes the surge, then that would be a good workaround. But I could see the issue lying more in the coolant driven side failing, or some other problem causing the computer to adjust erratically.


Another thought would be, is there a electronic controlled FIAV you could swap on, that doesn't have the coolant controlled valve?

I guess I've never been through it far enough to block off just the FAIV as it seems to cause the bulk of the problems from what I've found. A fully electronic solution or simply blocking off the FAIV would be a good solution to that problem and get rid of some coolant lines in the process.

I think I was mixing up my terms a bit, and see that the FIAV is referring to just the coolant side control. If you can block it off without blocking the ISC (electronic component), then I would definitely do so. Just make sure that your ISC (electronic) is still able to control airflow, and make sure to block off the airflow ports, and not just unhook the coolant lines.