I don't have many other places to turn to so i am hoping that someone here can help point me in the right direction. Every time i post here i don't get much response so hopefully i get something on this issue. It has been happening for a while now and i can't seem to pin point it. I will attempt to explain this as much as possible.

Some time ago i got tuned after i built the motor and upgraded the turbo. After the tune the car was running just fine. People that know me can vouch that i do not drive the car that often. Its an Evo 9 with 57k miles on the chassis and almost 1k since the build. I am on SD and stock ECU. So sometime after the tune i noticed my car was idling a little funny. initial start up would be around 2k rpm and slowly come down. i figured thats normal. AFR around 14.5 to 15.3 somewhere around that area. Driving around town car would consistently be around 14.7 to 14.9. First real issue is when i come to a slow stop my idle would fluctuate almost 500 RPM. It will bounce between 1k and 1.5k until i come to a complete stop then back to normal.

The second and bigger issue is my AFR when changing gears/ advance throttle more than about 30%. Like i mentioned before the cars AFR causing is good but when i give the car a little more gas than normal, i see my AFRS dip extremely low. I am not lying about how low. I can record my zeitronix wideband if need be, but we i recall the information on the wideband i have seen as low as 1.9. How it can get that low i don't know but it displays it on my wideband. I recently put a new sensor in due to my sensor dying on me. The car feels fine when i advance the throttle but the AFR has me worried.

I don't want to cause the cylinder wash down so i need to find out what my issue is. After my initial tune i took the car back to my tuner and he adjusted the ignition and it helped for a while but now the issue is back. I am suspecting maybe the front O2 sensor is on its way out, but i have not received a check engine light what so ever. I don't have a MAF so it can't be that. Please help guys.

 

General forum topics move so fast, that a thread like this can get buried quick. Posting in the Engine Mgnt forum would have been better as they soak longer up at the top & draw more of the tech crowd

I dont handle this forum otherwise I would re-locate it myself

 

Can I move it myself?

 

Does the car have cams?
What fuel?
What injectors?

Bouncing idle could be vaccum leak or a dieing idle air control valve.

The dipping rpm while coming to stop, can be normal for cars with big cams and big injectors.

 

car is on e85. Injectors are id2000. Cams are the cast gsc s2. The bouncing idle doesn't happen every single time. It just picks random days to do it. More often than not though. Also I don't really have the idle dropping. It never goes below the 1k. It just fluctuates between 1k and 1.5k.

 

Substitute witha good known iacv

 

I will try and track one down but what do you guys think about the rich conditions. I don't really know where else to look. I don't know how the car can go from running fine to being pig rich. something to due with the increase of throttle. AFR is good during cruise but anything over about 30% throttle and it's extremely rich.

 

Have you checked for boost leaks?

 

I had a similar issue. AFR was being inconsistent. Swapped out my cam angle sensor (literally a one minute job, it is one screw) and that fixed my issue. Part was $67.

 

How did you narrow it down to a cam angle sensor? Did you have any codes for it? Did you just swap all sensors one at a time? I have not done a boost leak test yet. I have to buy or build one.

 

What did your tuner say it is or might be or have you brought it back?
​​​​​​​What's your idle and cruise fuel trims?

 

i haven't spoken to my tuner. I have since moved due to being in the military. I plan on getting retuned but want to make sure my issue doesn't depend on a specific part. I don't have access to log anything so I don't know what my fuel trims look like.

 

Is there a way to tell what a good known IACV is? I see OEM cost around the $400 mark locally, and then aftermarket versions range from $22 up to several hundred...

Any advice would be massively appreciated as I am suffering from a low idle when the motor is cold...

 

Per the service manual you would need a multimeter to check resistance between pins on the IACV. People have had mixed success with aftermarket units. You could also check the junkyard and pull one off of an Eclipse. The IACV is interchangeable between Evos, DSMs, and a few Chrysler and Mitsubishi models so that helps widen your search.

 

Especially with a descriptive thread title like "Can someone please assist me"