I did a search and could not find a good solution. My evo 9 has a built engine/ ported cyl head, M2 272 cams, 65mm TB, ported IM, Intercooler, piping, cone intake, stock intake pipe, ralliart thermostat, red turbo and tubular header.

I had really poor driveability and idle/surging problems with a ralliart intake pipe. The problem went away the moment I installed the stock rubber pipe.

My problem now is the lean idle. It is between 15.3 and 15.8
Can this be caused from my ralliart thermostat? I have no boost leaks.

I want to log my 02 sensor. What values should it read in closed loop?

 

Has your computer been retuned?

Changing the intake piping (between MAF and turbo inlet) can alter the MAF readings (changed air flow).

Need to get a Wide Band O2 to read the AFR right.

 

I use to have a lean idle, then I found that I had a small exhaust leak before my Wideband O2. THis caused my idle readings to be off, but at WOT it was fine.

THe leak ended up being where the DP bolts to the O2 housing. Once I got that plugged/fixed, my readings went back to 14.7ish

 

i have an aem wideband gauge and checked the exhaust for leaks. it is fine. I need to figure out something else. Maybe idle rpm affects the AFR? My car idles at 1000 rpm. The idle maps in the ecu are stock but I do have a tuned rom. I noticed that when the car is cold and idles higher than 1000 rpms AFRs are closer to normal. I could increase the idle but I cant live with a 1200 rpm idle because my exhaust is too noisy.

I have messed with the BISS screw on the TB a lot to make my car driveable with the cams. Maybe the problem is there?

thanks for helping out

 

Hmm, I would get in touch with a stock ECU tuner like Mellon and see if he can take you a look at your ROM for a small fee.

From my understanding, a lean idle won't hurt anything. But, I would still get it checked out as I'm not 100% on that.

Good luck and you're welcome.

Good luck

 

I would set the BISS back to stock and have the idle tuned via the ECU so that it operates as it should with the cams.

 

thanks for the reply. Do you happen to know how many turns is the BISS screw backed out (from fully screwed in) in the stock position?

 

not off the top of my head, I'm sure it's been covered here before.

 

turning the screw should instantly make changes to your idle I would turn it until you feel like you are at the proper rpm range. My idle was messed up because of a cheap after market o2 and forgeting to put the gasket back where the dp meets the o2 housing. I had to turn the screw temporarly to make it drivable. After you feel like you are in the proper rpm range go back to check afr and make adjustments. Double check everything