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I've got a mysterious vacuum leak on my EJ20G that appeared after 9 hours of highway driving. The leak was real loud, very apparent. It seems to disappear when I get out of vacuum, but it might be that the engine is just that loud. For a while it idled horriblely, between 700 and 1500 RPMs, just bouncing. Sometimes it would hold at 2000. Now it won't even idle or it shoots up over 3000 and then comes down slowly and dies. The sounds is so loud that I can't pin down it's location between the turbo and the drivers side of the engine. I ran my hand around stuff and couldn't feel anything.

So yesterday I took apart the intake, the intercooler pipe out of the turbo, the BOV, and the PCV/breather lines right there. I came across a cracked hose from the crank case vent and fixed that. I found a small hole in the outlet hose of the turbo and fixed that. I also fixed the Greddy BOV I had because the adjustable screw was stripped. So after putting everything back together, it didn't fix anything. It's real hard to pinpoint the sound because on the engine sound, but the BOV is venting a lot of air at idle.

It all happened suddenly too, which is even worse. It wasn't like I did something and when I started it up, it was making this sound.

I also took of the IAC. That seemed to be fine. I might clean it anyway, but it wasn't obstructed at all. I don't have any codes either. I'm using an Apexi Power FC.

Brent

you can find a vacuum leak by spraying suspect areas with carb cleaner. if you spray some area and it starts to run better, there's your leak.
also clean the crap out of your IAC with some carb cleaner.

I'm gonna clean my IAC real well, but I'm really beginning to think it's the BOV causing all the problems. It's pushing out more air than normal.

Fix your BOV or replace with the stock BPV. You know you have a leak right there. Why look for another one until you fix that. Maybe that's causing your problems.

I'm trying to locally find another BOV I can test, but I don't have a stock one I can use with my FMIC.

I cleaned the IAC and it didn't help. I can hear the IAC buzzing when my key is turned to ON. I tested the wiring on it also. The center is power, the black wire is grounded, and the 3rd wire had a very very weak ground.

Brent

While you're troubleshooting, I think you should plug the blowoff valve. If nothing else, put duct tape over its outlet. Your turbo will survive if you are very ginger with the throttle. At least do this when testing at idle. A stock ECU will never idle right with a BOV open. And like Josh says, the blowoff valve is quite possibly the sole culprit.

I recommend using starting fluid rather than carburetor cleaner. It's more volatile.

I don't have a stock ECU, I've an Apexi Power FC.

I put a different BOV on and there was no difference, so now I'm gonna try a different IAC.

At the IAC, in the manifold, there is that rubber piece and then the flat circular thing set in there. What are they for? Is it possible for the circular thing to not do it's job?

That's a check valve, so positive pressure doesn't flow through the valve back into the intake.

Ok, I think I found it and it was a vacuum leak. So I've got a question. Right infront of the turbo there are 2 hardlines. One has the hose for the fuel going into the regulator. Under that is a vacuum line from off the intake manifold. Where does that go? It was broken under there. There are 4 vacuum lines off the manifold (excluding brake booster): on the throttle body to the charcoal canister, bov, fpr, and mystery #4. The one to my fpr is t'ed to, I believe, the pressure exchange solenoid.

Any problems with any of this?