So this used to only happen when I would take it through a car wash, and I would shut it off while in it, but what it would do after I started it back up was the rpms would drop down to 500 for about 10 seconds and go back up to 1200 and then back down and so on and so forth. At the same time my wideband would be reading 18 the whole time. I would just stay parked and wait for it to subside which usaully took about 5 min at the most. However now its starting to do it all the time. But it only seems to happen when I shut the car off and come back to it 5 min later and start it back up. On a cold start it does fine. I already changed the plugs to see if that would help but it didn't. But they needed replacing anyway. As of right now I put sea foam in the tank to see if that would help cleaning the injectors. I can't tell if its working yet because today the rpms didn't drop but my wideband was reading 18 while the car was vibrating. I have no idea what could be wrong with it. Driving it around its fine but only at idle it has this issue. I'm fairly new to owning an Evo and still learning. Any help on this would be awesome!!!

 

18 is way lean. idle should be like 14-16 IIRC. I don't have a wideband so I can't tell you exactly

injectors and fuel system would be the first troubleshooting issue. are the AFR's while driving normal?

 

yes under normal driving it sits right at 14.7, and under full boost its usually right around 10.8

 

Check the Idle air control valve. Them failing is somewhat a common problem from what I have seen. 18 is lean too so as ||Demon|| mentioned check fuel system also.

 

Where exactly would I find that?

 

Where exactly would I find that?

 

https://www.evolutionm.net/forums/ev...id-inside.html

 

UPDATE

Changed out the IAC valve about 10 min ago. Turned the key to on so the ECU would reset it. Started the car up and is still kinda having the same issue. It doesn't vibrate anymore and doesn't feel like its idling rough but it sounds like it a little bit and my wideband still reads at 18.0 when its happening. but now it only happens for a split second then goes away. Also now it was idling at 2100 and wouldn't drop down. I heard you have to drive it around for a bit to let the ECU settle and relearn how to idle properly. I'm gonna clean the MAF, TPS and throttle body next to see if that will help the issue.

 

Check to see if you have a leak in your throttle body

 

After replacing my IAC it took driving it around for most the day before it settled out.

 

Sounds like a combo between stuck throttle body and fuel system issue.

 

just cleaned the MAF and Throttle Body. Also I adjusted the BISS screw one full turn to the right. Mad the rpms drop to about 1700 at idle. I know that some people say not to mess with it without evoscan and some say its fine. So I did that and its still doing the same thing. If I go to start it 5 to 10min later after it was just running my wideband goes up to 18.0 and my rpms will drop and the car will shake. On a cold start it does fine. Oh and also today before I did anything to it it didn't want to start at all unless I gave it gas.

 

So now today the car will not even start. It was very low on gas so i thought that might be the problem but nope. It cranks fine still but wont catch. Changed the IAC valve back to the old one but didn't work. No idea why it would just stop working. Any help at all would be awesome

 

Do you have power on the interior? radio, lights etc? If so, how are your battery lead connections? How are you plugs? I changed mine to plasma coils and have had much more stability. Starter? Fuel/air sensor issue?

 

Did you check for Vaccum leaks also... That could cause your low idle also the iac are funny mines was doing the same thing i took it out and cleaned it put it back and it was fine... Check for leaks at the throttle body