I've been messing with my idle for over a year now off and on, and its starting to really **** me off. I've had 2 different tuners play with the car thinking it has be the tune, but both of them say there must be a mechanical issue. So $1,200 later here I am. Today I checked the IAC stepper, and it is working as far as I can tell. There are no boost or vacuum leaks, which I've checked for several times.

Now I'm wondering if the little choke under the IAC stepper could be stuck open, causing the car to idle so high. By stuck open, I mean not closing off when the water temp heats up like its supposed to. Does anyone have any experience with this little choke, and know what the symptoms are when it doesn't work. In order to get my car to idle at 1,100 rpm, the IAC is at 15-20, which is obviously way too low, so I know there must be a leak in the throttle body somewhere.

The only other thing I can think of is the screw on the bottom of the MAF. I have no idea if that could even affect the idle, but mine is screwed all the way out flush. I have a hard time believing this could be the issue though.

 

After doing some reading, I found that the choke I'm referring to is called the Fast Idle Air Valve (FIAV). I'm going to pull my throttle body for the 10th time to see if that could be the issue.

 

I pulled the throttle body off and pulled the FIAV out. It is definitely damaged, I just don't know if it is causing the high idle. I don't really get how this system works, because it looks like its metering the same air as the IAC stepper motor, which doesn't make much sense to me. Now I need to figure out if I can buy these parts separately.

 

how do you know its damaged?

 

Replace that o-ring. I had to put high temp sealant near the top to stop a leak I had around there.

Have you set your biss with you IACV off? Have you tried borrowing a IACV? I'm on my 2nd IACV on my 90k 03 evo.

 

I know its damaged because that spring is supposed to be uniform all the way down, and the last two coils are kinked. I'll make sure I replace the o-ring.

As for the IACV, no I haven't replaced it. I did however turn the car on with it taken out of the throttle body, and it did extend like it was trying to control the idle. That made me assume it is working fine. What do you mean by setting the BISS with the IACV off? If you mean Actuating the SAS in evoscan, yes I have. When I hit that actuator nothing really changes. My BISS is turned all the way in, and it still idles at 1,100.

 

You're supposed to stack the clips and reinstall. I have to look at my other TB tomorow.

 

You'd think the stepper motor is all that is needed to control idle but Mitsu has also used a FIAV since at least 1990. So, yeah, that could be the cause of the problem.

 

I know mine is bad, but just to check if this is what is causing my issues, I bent it so that it will always be in the closed position. I'm going to put it back on tomorrow morning, and I'm hopeful this takes care of a year long problem. If it doesn't I'm going to order a new IAC stepper, because mine has 113,000 miles on it. I read that those have 4 different coils in them, and they can still seem like they're working even though they are not working fast enough.

 

So what does your car idle at?

 

Did yo ever find out what the problem was. My idle high and I have a check engine light on too.

 

When I turn the wheel the idle goes up another 1k rpm

 

FYI you can check the resistance across each coil on the ISCV. I'm not sure if they match the DSM ones, but there is a guide on the vfaq for checking them.

 

I used to have the same problem with my Evo. Only the '03 Evos have this problem that I am aware of.

when my iscv failed, I upgraded the throttle body to an '05 which doesn't have the FIAV port. All that does is blow hot gases from the EGR onto/near the isc which can/does cause premature failure of the ISC.

Since upgrading, I have not had any problems with the isc.

 

did you ever figure this out?