The car is a 2003 Evo 8.

880cc injectors
Non-Recirc BOV (will be change this week)
HKS 280 cams
Magnus Intake Manifold
Stock Throttle Body
Tuned on ECU Flash

The car idles fine for the most part, it only has problems when the heater is on and it is on the Defrost setting, or Defrost and floor. If it is only on the floor setting it will idle normal.

As soon as you put the setting on the defrost or any combination that includes that the car will start idle surging really bad between 2.5K rpm and 3K rpm.

So my question is this. Is the vetalation control ran by vacuum from the motor?

And if so where is it coming from.

If not, I am just looking for ideas to check so the car doesn't go nuts when the heat is on.

 

Defrost uses the A/C. When the A/C is on the engine ECU ups the RPM to compensate for the increased load. I'm guessing the idle has already been messed with to accomodate your cams.

 

It has been, but not enough to make it go crazy like that. It isn't my car, it is my little sister's car. So I am just trying to get it to idle better witht he heat/AC on.

So I am guessing I have to lower the idle stepper for when AC is on.

 

Im not sure it this makes a big difference but I just switched out a turbosmart BOV in favor of the stock due to the fact it would cause my idle to surge a bit, I change the open air BOV, they seem to confuse the MAF!!

 

did u just recently pull the neg batt term? if so, that could cause it because the car has to relearn it's idle. with cams, its a huge issue, takes longer and idles lower but no worries, let it idle with the ac turned on for about 15-30 min and then drive around to see if it has changed. it should learn the "idle" by then. if not try it once more (i noticed sometimes it takes a couple times of idling then driving for the ecu to learn)

also, do u have a mini batt? if so, that could also cause it. i noticed when i switched out my regular batt for a mini batt that idle was lower and it had less power (idled lower) when the ac was turned on as compared the my regular batt, idle did not change at all. (this was after letting the ecu relearn everything)

if none of these apply to you, change your idle RPM in the ecu a little higher. i have mine set to 1000-1050 for without and with AC. idle RPM starts at around 700-800 on a stock ecu (i cant remember what exact value it was)

 

All actually apply except for the battery. It has been running for over 2 weeks like this. So it has had plenty of time to learn the idle. I already have the idle turned up to 1100 - 1200 depending on the temperature.

It does have a battery relocation to the trunk, I think it is a stock sized battery though.

By the time I touch the car again the BOV will be recirculated and a little vacuum leak will hopefully be fixed. The only problem is, we have no idea where it is coming from. You can audibly hear it when the car hits a certain RPM or idles up, something is letting air escape. But I am not really sure what or where just yet, as I did not do the work with the intake mani install and have limited time with the car.

 

Indeed an open air bov basically lets the already metered air out of the system and this can cause problems with a MAF car. So hopefully the BOV gets recirculated the next time I see the car.