EvoM i need your help with an issues ive been trying to get figured out.

Keep in mind this happens mainly after Ive been driving for a while or if i went hard on in (Like a 3rd gear log pull).

So after i come to a stop and let it idle the RPM drops for a second and my AFR goes super RICH, then it goes to normal.

It happens very randomly and in no particular pattern.

I have a video & log if it helps.


MODS IN SIG

 

vid added

 

Do you happen to have a vta bov? I know it isn't in your list but not everyone list a dv/bov.
Have you also done a boost leak test recently?

 

i have a stock evo 9 BOV..
And yes i did a boost leak test and one of my injector seals (one going to manifold) was leaking under boost but didn't think it would affect idle due to no pressure build up.

 

Are you tuned to open or closed loop idle? Did this just start or has it been happening?

 

closed loop idle. and it happens even when i put my stock map sensor on with a stock map

its been like this for a while now. but like i said it only happens if i get on it hard or after long drives..

 

I'm guessing its your front o2 sensor crapping out. If it happens on wot pulls (high heat) and long drives (constant heat) on the front o2. That's a stab In The dark though. Or maybe the iac.

 

is there a way to test the front o2 sensor? they are so damn expensive i dont want to buy one and it not be the problem.

 

nvm i found some that aren't so expensive.. i shoot flames sometimes from my exhaust how bad do those mess up o2 sensors??

 

Rockauto.com had them cheap, but before you go throwing parts at it.

Are you on a mini battery???

Can you hear the fan kick on then it does the sweeping and idle dip?

I had this issue and it was my fan kicking on and pulling voltage then my AFRs would dip. I switched back to full size and these little things went away.

I would log battery voltage and see if it dips when the AFRs start swinging. Or get it op temp then slam on the A/C full blast and see if it replicates the problem.

 

I noticed in the video your dash lights go dim when it happens....

 

cuz it drops in rpm so low almost to a stall so the alternator doesnt have as many revs on it.

 

Like the other guy said, its when your fan kicks in. Mine does the exact same thing at idle, fan kicks in and idle drops sometimes almost to point of stall. Only does it if I have the heater/ac on, when it dips i switch the blower to off and idle jumps right to normal!

 

i didnt hear the fan kick in though :-/

 

Maybe you could try driving the car till full operating temp, pull over and let it idle, turn the blower on to the first setting set to defrost then wait for the engine fan to kick in to see if it drops? Its really bugging me too now that I think of it, mine is definitely power drop when the fan kicks in with the heater on! Maybe my battery is on its way out as it is the original from 06 lol