So let me start from the beginning. I recently upgraded my Intercooler to the monster 4" made by VRSF. At the same time I changed my Synapse BOV to a Synapse DV. I also changed my injectors from RC1200's to FIC1450's. Dialed in the injectors and ran into some problems. Car idled like **** and would stall when not in gear or holding the rpms up. Thought it was the injectors, ruled them out. May have been a boost leak I'm not sure cause I tore everything apart at once. Fixed that. Then yesterday I went for a little cruising, hit WOT a couple times and then my CEL came up with a P0505 Idle control circuit. Researched and found it could be a vacuum leak or a gunky throttle body. Tore into the throttle body today, cleaned it all up. Found a lot of oily smudge around the flapper and behind it. Cleaned all the vacuum lines into the IM as much as I could. Car runs pretty good now and with no code.

What I've noticed is that my vacuum reads a little bit lower than normal while cruising. At idle I typically sat around 18-22 depending on the day I guess. Thats pretty much the same but stays around the 18 mark a little more, maybe its just that day. And also when I decel, downshift, in gear, coming to a light like, it reads 24. Which is normal. But when I'm cruising it seems to be about 4-6 psi off. Cruising usually on a flat area about 1/4 throttle I would typically get 18-20.. Now I'm getting 12-16 psi, and of course less and less the more I get it throttle. And I say that in a gradual manner, not hammering on it obviously. Could this be do to a vacuum leak? Doesn't make since since my idle is about normal. Thought it might be a boost leak but I'm hitting 18-19 psi just fine. Could this be because of the new bigger intercooler? I'm on a basic tune btw, but I don't think a tune would effect the vacuum, or am I wrong...?

Thanks in advance

 

Update. P0505 came back

 

Evo 8 or 9?

 

Evo 8

 

It could very well be because of the bigger inter cooler. Since it's bigger it takes more to pressurize it.

 

After some research found some info on p0505

Probable causes:
1- Vacuum leak on the engine
2- Dirty throttle body
3- IAC motor is defetive
4- Poor electrical connection to the IAC valve.

someone at mitsubishi has told me the code comes up from carbon build up in the idle control valve

what you do is take the valve off (just under the throttle body), clean it thoroughly and then put a bit of grease on it before you put it back on. if you dont put a touch of grease on, the code will come right back.

if you do it properly the code will go away