Originally Posted by 304MR

I just checked my logs and I'm not getting anything on my fuel trims. I figured it was primarily o2. Changed with Denso version and still nothing. Weird thing is I only get a random misfire code (no other cel codes for bad o2).

Maybe shell out the $350 for the oem o2?

Originally Posted by turbotaloon95

First and foremost, I'd like to make this thread an intelligent discussion and an informative post.

Second, I am in the preliminary stages of figuring out my idle issue. I can still get the car to idle and run fine to get me back and forth to work and wherever else I need to go. I have another project car taking up garage space and need to finish it before the evo goes in the garage for some upgrades
and troubleshooting. This means I am just looking to line up diagnostic steps and things to look for before I can provide any feedback.

So here is some back story. The car is a '03 evo 8 that is 99% stock. However it has a walbro 255 and 850cc injectors that I installed a while back. I have tuned it through ecuflash with the latest tephramod rom. With some help from the forum members, I got fuel trims locked down and very close to zero. Otherwise car has a full TBE, K&N air filter and I'm usually running like 25psi on the stock turbo through a MBC and upgraded wastegate. I also recently removed the EGR valve and installed the block off plate. I turned off all egr functions in the ecu.

The car starts up exactly as it should when it is cold. The problem really happens when I try to start the car when it's warm. It starts and catches, but will stumble at like 200-300 rpm, then after a few seconds, it kicks up to 800-900 RPM. An additional, and I believe related, issue is that during idle sometimes the AFR will sweep from super rich to super lean or vice versa. It eventually settles back down to stoic. Drive ability seems to be fine. Sometimes it will stall if I throw it in neutral and come to a stop while turning the wheel or something. Otherwise in boost it feels ok. Sometimes I get knock in the low RPM range when the load is high, but I think that's a tuning issue.

I haven't done a boost leak test, but I've sprayed brake clean around the intake while running to see if there were any obviously leaks. I found nothing. The throttle body was rebuilt like 3 years ago with mil-spec seals and new screws in the throttle plate. T bolt clamps around the intake pipes. BISS was set appropriately with evoscan. Idle is set to 800 rpm.

I have the theory that my FPR is going bad, but I'm not sure how to test that. So again, I wanted to see what you guys thought and what diagnostic steps I can take to help determine the cause of this issue. Thanks!

EDIT: Oh, and I replaced the IAC module earlier this year with a new OEM part.

Originally Posted by turbotaloon95

Thanks for posted here and reminding me I had this thread!

Long story short, I found out my IAC motor was ****. I had replaced it with an aftermarket unit not long before I made this post. I replaced it with an OEM Mitsubishi unit and the car drives 100% better.

Originally Posted by kaj

I got two from the junk yard. All three seemed to work the same. Maybe they were all bad LOL.

If an OEM one weren't so much $$$$ I'd give one a try LOL.

Originally Posted by turbotaloon95

Yea, I think I paid something like $300 for a new OEM IAC. I tried to save money by getting an aftermarket one but I think I still paid closer to $200 for it. So in the long run, I would have saved time and money by just getting the right part.