so im de emissions-ing a spare harness i have laying around for the build im going to do. is the bac absolutely neccessary to have the car run right?
FYI build is a street port on stock internals and header baack exhaust. stock intake mani(maybe port matched)

 

No, it is not "absolutely" necessary but it sure is a nice thing to have.

 

It helps stabilize the idle when you put electrical loads or a/c loads on the engine. You don't need it, but then you will want to set your idle a bit high to compensate for it.

 

do yourself a favor and leave it on, I removed mine and will now proceed to put it back on.

 

Leave it on. You can ditch the coolant lines if you want to clean things up a bit. The metal passageway even unbolts from the body of the BAC.

 

 

alot of vehicles have these and they have no coolant going through them.
I am installing a IAC from a Ford and will be using the aftermarket ecu to handle it

 

^ A bit of over-engineering on Mazda's part, IMHO. Unless you live in a frozen wasteland, your BAC will be just fine without the coolant passageway.

 

if you read through those two pages I posted carefully, the BAC was designed so that the coolant hoses would use water to set the temperature of the magnet/coil inside the valve. Then the ECU would adjust the BAC valve duty slightly based on water temp, because the temperature of the coil affects its operation some. But honestly I don't think it makes a noticeable difference. Over engineering is correct.

 

Yeah, it says that right at the end. I'd seen those pages in the training manual before, and opted to ditch my coolant lines awhile back. Also, the engine bay heat will bring the BAC up to temp even without the lines, but it won't stay as constant as it would with water running through. The difference is not even noticeable.

 

hey thanks guys i just didnt want to delete something that actually is worth leaving on.

 

I removed mine and have no complaints. Idle is set at about 900-950, it dips a touch when I crank the heat.

This is what I used for deleting the BAC.

 

You don't need it. It can be helpful in a somewhat stock configuration but you don't absolutely have to keep it. If you have a/c and p/s it's probably best to keep it with a stock ECU. I took an FD TB. FD UIM and S5 LIM and am running it all with a Rtek2.1, deleted the secondary throttle plates and BAC, all emissions and extras removed. I did notice that the new setup flows substantially more air at idle, but it was easy to correct fuel/timing for new manifolds. I don't think BAC maters much if you compensate with higher idle, the BAC just helps you not stall at low speeds.