My evo 8 has a terrible idle when cold. It will idle so low that it just ends up stalling. As the engine warms up, the idle stablizes and idles very smoothly. Car is stock except for TBE, LICP, and MBC. Stock intake and UICP. I replaced the Iacv and it had no effect. Same problem. I went into SAS mode in ecuflash and set the base idle and its the same. I dont know what else to try???

 

What is TPS percentage set to at idle, what are the AFRs, this is a MAF car I take it?

 

Yes Maf, tps at idle is 12-13%. I dont have a wideband as of now. I was planning on getting one in the next week or so. Do I really need a wideband to diagnose this?

 

Have you done a boost leak test to make sure it's not a small leak somewhere after the MAF?

 

the other thing that could cause this, least in my experience, is a dead O2 or lazy O2 that keeps it in open loop when cold and DEAD lean. It sorts itself out when warm since a stock injector car will run at the same AFR when there is no O2...more or less.

 

May need to mess with your idle settings based in coolant temp. I had similar issues years ago and upping the values based on coolant temp fixed it.

 

Try changing you oxygen sensor!

 

Log o2 sensor signal before replacing it to see if it's working normally or not. The signal should continually cycle from rich, to lean, back to rich, etc.

 

Ill try logging the o2 today and see what happens.

 

The sensor is reading from what I see. Startup it's 8-12% and then start to lower as it warms up to between -2% ~ 3%. Should I just try messing eith the iac steps?

 

I meant to log actual o2 sensor voltage, not the STFT. Sorry, my fault for not being specific.

 

what should the voltage be readuing at idle? I actually just got a wideband and the AFRs are very lean at idle. Going as high as 17-18 at idle. It will get rich around 12 randomly for a few senconds and then back up to 15-16 most of the time. Thats at normal temp idle. Initial startup/Warming up its so lean it sometimes wont even read on the WB.

My AFR map is 14.7 at 500RPM and 1000RPM,

 

it should constantly go from .1 to .9, then back to .1, etc.

 

The voltage cycles from .1 - .8 when warmed up but right at startup it stays around .5 - .6

 

does that indicate that the o2 might be faulty?