I've been having a new problem with my car. After it gets up to operating temp, it will occasionally start to idle really rough when I come to a stop, it almost sounds like it has cams (which it doesn't) or sort of like it's running on 2 cylinders which I experienced when I was making my COP setup (pins were not pushed all the way into the plugs, fixed it though). Again, this only happens when the engine is hot. When this is happening, it seems to run OK at highway speeds and under boost.

The most notable thing I think is that the vacuum jumps from about -20 (where its at normally) to -10. The idle dips to or below 500, and it really really wants to stall. If I give it some gas the idle jumps back and its fine for like a second then it goes back. Also, if I shut the car off for about 5 minutes that usually fixes it, only to have it happen again the next time I come to a stop.

I noticed this happening, and the only thing thats changed since its started is that I swapped my greddy BOV (recirculated) for an oem evo 9 one (recirculated), and I installed my COP setup. But, its been almost 3 months now since I did those things and this only started happening about 2 weeks ago.

The most recent thing that I did was install the stock exhaust again (only from the catalytic converter on) for emissions...It seemed to start happening shortly after that...however I drove with the stock exhaust on for the first year of owning the car and I never had this problem.

I removed my COP and returned that to stock, that didn't help. I also just did a boost leak test, only leak was a small one on the LICP.

 

Forgot to mention, this is also with the A/C off! Can't figure this out.

 

Anyone?? It's driving me nuts!!

 

needs a tune maybe? or some fresh gapped plugs.

 

check your idle air control valve on the throttle body. and your map sensor. the synptoms sound similar to mine, one time was IACV and the other was the map sensor. hope this helps.

 

I'm 90% sure my iacv is going. A lot of the time when I coast to a stop or something like that the car can't catch the idle. So it like dips to 400 then comes back up to like 1200 and settles. It's stalled a few times because of this. Map sensor I didn't consider! Thank you. I think I'm going to order a replacement iac tonight and go from there.

Plugs were done within the last 3k miles, I think they're fine. Tune it definitely needs but it only arose recently so I doubt the tune is the issue.

Thanks guys!! Any more suggestions are always welcome!

 

If you can find the issue to this, PLEASE let me know. I'm actually having the EXACT same symptoms as what you just described as well as going through the same methods of swapping parts. Upgraded with COP and everything seemed fine, but after several months, car had same symptoms as you described. Swapped back over to OEM plugs, problem went away, but seems like it is slowly coming back. I don't want to swap out sensors after sensors to find out it's not the right part to swap. If you can let me know what you swapped for the fix, that would be a great starting point for me as it seems identical to my own.

 

Sounds like an issue i had. It would always drop idle at lights and run rough. make sure to check your coolant, have you noticed any loss in coolant? dont just check the reservoir but the upper hose to make sure its properly circulating and holding pressure at the radiator cap. Also thermostat, because when i had this issue i neglected it and eventually it overheated when i had a stuck thermostat and leaking water pump= head gasket!!!

 

What a coincidence! Haha I'll update when I get the new iac it's supposed to come today.

In the mean time, I removed my tb, and removed the iac. I plugged it into the harness and had a friend turn the key to "on" and watched the iac as suggested in another thread. It moved out slightly, then started clicking a few times but the plunger was not moving from what I could see. The whole unit started to get warm as well. It moves back in when the car is turned off. The o ring was fine, the part that enters the tb was a little dirty but nothing crazy.

The only other thing was that I looked at a picture of a replacement and compared it to mine. The replacement on the end where the plunger is has like exposed spring, when I took mine out..its different there's no exposed spring it's just metal cylinder with the plunger at end...and I couldn't remove it..and I couldn't clean inside of it. but I'll put the replacement in anyway when it comes. I'll be sure to update.

 

Sounds like the IACV to me, but if you replace it and are still having the issue. Check out this thread it might help, if you have cleaned your throttle body.

https://www.evolutionm.net/forums/ev...e-sealing.html

 

Ok one issue...the IAC pulled out of my car looks like the first file attached (the one with the red evo behind it) and my replacement looks like the other one with the exposed spring....my car is an 03 if that matters. Will the new one work? And yes I ordered the right one...

 

It should work, I believe its a revised part, but then again I've been wrong before, worst case is it doesn't work and you return it. Im pretty sure it will. Keep us posted and good luck with your repairs.

 

lol You're telling me. I was having this issue for a bit, but the problem is that it doesn't ever occur until you drive the car for about half an hour. Every time I took it to the mechanic, the problem disappears, thus nothing to "fix". Originally I thought that it might have been the COP setup, but that kind of felt like it fixed it when switching back to stock. Only issue is that the problem started coming right back after a couple days later. Sometimes it feels like it's getting worse and sometimes it doesn't. Well good luck on your fix though. Hopefully whatever solution you come up with will be the same issue for mine since it sounds so similar in almost every way. Actually going to the mechanic now and suggest the IAC and see what he thinks as well. I'll let you or anyone else know if I have any positive results as well. *fingers crossed*

 

Replaced the iac. The part works fine, but it did not fix my problem...

 

So have you thought about setting the computer? Your tune I am thinking isn't doing you any favors either---you can't go from tuned free flow exh back to stock and have everything run rt--as you are experiencing. Pull the battery cable and let it sit for a while-- and see what you get, it will take a day to 2 to adjust-- Good Luck.,