As I understand it the JDM UIM has no port for the BAC to feed air to control the idle under load. When the a/c comes on it slows the idle sometimes killing the engine.

So I was wondering what the options were. On the 91 MR2 turbo they have an adjustable valve that is turned on with 12v to increase the idle by letting post AFM air into the intake manifold. I think thats basically how the S5 BAC works too.

Would rigging a Toyota valve relayed off the A/C clutch wire increase the RX7's idle too?

Are the other, easier options?

Thx

Jim

 

One way I have seen recommended is to set the idle up at 1000 rpm (kevin landers@rotaryresurrection sez). Supposedly at 1000 rpm the drop for A/C is not a problem. I wouldn't do that on a USDM car with BAC, but you have a different circumstance.

 

How much is the idle going down by?

 

Cool, Jack. We'll try that.

Incubu, it drops about 200 - 250 rpm. But often it just dies at stops if the a/c is on. It's 103 here in Austin so a/c is kinda important!

 

I have a different bac in my car, mounted on the firewall, I used one off a FD



I currently have a JDM UIM but I filled the holes for the bac in because i did not want that hideous thing on the side of the intake, so I am not sure what you mean by your uim does not have the holes? Maybe someone put a block off plate on there?


BUT I am swapping over to a S6 UIM because I can then hide the BAC under the manifold

 

The s5 JDM UIM does not work with the idle adjust screw on the BAC. The idle adjust screw doesn't work, so you won't have that additional source of idle air. The BAC valve itself (the air that flows through the spring loaded, duty controlled valve) still works.

 

What he said. To help clarify. On the JDM BAC there is no adjust screw and also on the JDM UIM there is no port on the manifold. You can't swap to a USDM BAC if you are using a JDM UIM.

LOL well I take that back. You can put the USDM BAC on there and turn the screw all you want if it makes you feel like you're doing something

 

Ok, so let me see if I have this right by summarizing all the input...

I have a USDM BAC on a JDM UIM - all S5. So, the BAC should be functional and should be increasing the RPMs under the command of the ECU whenever the AC is turned on.

The BAC's idle adjustment screw will do nothing so the only way to set the base idle is with the stop screw on the throttle body.

And if the idle isn't increasing when the AC is turned on, then the first place to start looking is the BAC to make sure it is working.

All sound about right?

Thx!

 

if your BAC was operating correctly you would not need to adjust for the AC, it would do it for you no?

Jspec cars dont crap out when you put the AC on

 

I was just playing around with my JDM S5 Tii's BAC valve over the past couple of days and found a few things. Firstly, when it's on and connected the idle does go up by about 100-150rpm or so, which is as expected. However, with it off, even with the car under full load (turn signals, high beam, A/C, radio, hell I even turned the interior lights on!) the idle didn't really drop by much.

So mine has been permanently replaced by the blockoff plate.