i have two questions:
ever since my buddy installed an injen CAI on his '08 Evo X, he's getting a BOV flutter when he releases the gas pedal-is this harmful for the car? if yes, how does one get rid of it? he's running the stock BOV.
also, he installed a speed circuit test pipe and got a service engine light, although the website and other users claim they didn't get one. does that mean the o2 sensor wasn't installed right? THANKS IN ADVANCE!

 

You will always have slight BOV flutter at low boost because the turbo did not build enough boost to pull the piston consistently so instead the pressure is tapered back half out the piston and half back through the turbo. If it flutters at high boost then there is something wrong with your BOV. One of the reasons why you start to hear the flutter when you never heard before is that a open air intake will make the BOV more audible as that there is no sound denting housing muffling the BOV when it discharges like the stock airbox.

CEL with a test pipe is common if you do not have a O2 bung fix like Touge Factory's 90 degree elbow bung.

 

thanks! i think speed circuit has a bung-fix, don't quite know what's going on here

 

The O2 spacers don't always work. Have you verified it is in fact an O2 sensor CEL that's being tossed?

I was never able to get rid of my CEL-via-O2-sensor, and I tried every mechanical fix; 90 degree angle, 45 degree angle, spacer, etc.