Hello Evo Family,

I've read threads about idle issues, but have not found a good answer yet for me to be able to fix this issue.
I'm sure other people have fixed this issue, and I would love to know what was the problem and how it was fixed.

Here is the Video:
https://youtu.be/dGabqszmoeE


After warming up, and driving, and coming to a stop light the idle dips and almost stalls and then corrects itself, but it's very annoying. I noticed that the Vacuum drops from the normal -19 inHG down to -10inHG when the idle is having issues. After it auto corrects itself the vacuum goes back to -19inHG.
It also happens when putting it in Neutral, or when slowly turning, or trying to drive up on the driveway. I have to give it extra gas so it will not stall. Sometimes when I am about to park it, it just stalls if I don't help with extra gas.

Evo IX MR is on Tephra V7, E85, tuned, stock cams.

It's been doing this for about a year or so, during the summer as well, so it's not the fuel.
Spark plugs are new, I cleaned the MAF, cleaned the ISCV(Evo IX has the one with the spring) , it wasn't too dirty and it seems to be working.

Did a boost leak test, and no leaks in the piping.
The only slow leak is coming from the valve cover exit hose by the battery that goes back into the intake pipe. But I believe this is normal on all Evos. If I vice grip that hose, it stops leaking.
I'm starting to think it could be from the EGR system turning on, since that is connected with a bunch of vacuum lines to the Intake Manifold. I checked those hoses, and they are all connected.

Thanks for your time!

 

Might be the idle air control valve on its way out,

 

I found something new today that causes the idle problem directly. I believe it is EGR related.
After a warmup run, getting the car warmed up to temp, the idle problem started again.
I noticed that if i rev the car from the throttle body by hand and let it go and let it stabilize, it has a shaky idle.
Now, if i clamp down the two small hoses from the top of the throttle body, while reving it by hand, the idle works great and doesnt dip the idle below what it should be. Essentially, i am plugging the vacuum leak that is happening.
I cleaned the egr valve (wasnt too dirty), i put zip ties on all small vacuum hoses and, the problem is still there. It could be that the EGR system is remaining slightly open and not operating correctly and creating this vacuum leak. I dont think this problem is at the egr valve, but some other EGR component.
Those two lines go behind the intake manifold to what i think is the egr control solenoid, which could be faulty.
Anyone replace that part that has 3 small vacuum lines connected to it?

 

Maybe the solenoid is stuck open allowing constant vaccum.

Or possibly the hoses might be routed incorrect.

 

Idle Issue is now completely fixed.
It was not the IACV, I replaced it with a new one and the problem was still there.
It was the EGR system, which was unexpectedly opening at idle after car warmed up.
FYI, to test if your EGR is opening a little at idle, just pinch the EGR valve vacuum line by hand, and see if the idle improves. If it does, then it's a problem in the EGR system causing it. EGR should be closed at idle.

 

This post was helpful. My '11 Evo X suddenly started to idle rough did some inspecting found the maf sensor housing slightly cracked and it was not allowinge the maf to seal correctly threw a code ordered the new housing and I suspect that will fix it if not I am going to try your egr test.