can you adjust the BAC on a 89 gtu N/A?? i kno thats how you adjust the idle on a turbo. whenever i plug the BAC in my rpms goes up to 2000 idling. or do i plug in the BAC and adjust to TPS screw that the throttle is less open???

 

IIRC the S5 BAC has no adjustment. The idle adjustment is in the FSM. Its the best way to go about adjusting your idle.

 

What are the rpms when the bac is not connected?

IF the rpms are under 1000 rpm, then I'd say the bac is the problem........maybe.

With the key to ON, does the bac vibrate?? As in click, click, click on and on and on?

If it is vibrating, then you might try removing it and spraying some carb cleaner into it and then dumping the fluid several times. Do not pry on the diaphram or you'll ruin it.

You should be able to remove the bac.......connect the electrical connector to it......turn the key to ON, and the bac vibrate. While it's vibrating you could spray and dump.

Or remove it and fill it with carb cleaner and leave it overnight and then dump the carb cleaner.

If the bac does not vibrate and you see the diaphram inside go and stay full open, then I'd say it's a wire problem of some sort.

 

the BAC is on when i turn the key. i hear it. it has already been cleaned too.

 

I'm S4 oriented. Is it possible that on a S5 there is another item like maybe the VDI or???? that is vibrating?

So if the key is ON and engine running, you can go to the engine bay and pull the bac plug off and the idle goes down to???????????what???????????????????

I'd say the bac is toast if you've already cleaned it. Maybe damaged it (diaphram) when cleaning?????? Didn't turn any of those allen screw/bolts on the ends, did you?

 

the car idles at 800 rpm's when i pull the BAC plug. i tried like 4 different BAC from the mechanic. it's wierd. my car will only idle correctly when the BAC is unplugged. but it start fishing when you put an electrical load on it. like turning the steering wheel all the way one way or turn on the heater or defrosters. and i didn't adjust any bolts or screws on the BAC. btw what's a VDI??

 

vdi IS part of A s5 inTake.

For some reason that I've no clue about, it seems the ECU is driving the BAc to full open. If you've tried several bac and they all do the same, it SEEMS to me it is the ECU that is the culprit.

One thing that will drive a bac to full open, at least on a series four, is the ECU seeing a START signal when the key is to START. When you go to start on a S4 the ECU gets 12vdc on pin 3B. I assume a S5 works the same. It's an unlikely scenario, but something that would cause the bac to go full open.

I'll just drop out of your thread. I think it would take someone to put a meter on the BAC's input from the ECU to tell what is happening, OR maybe just a visual by connecting a spare bac to the harness while the car is running and leaving the stock bac bolted to the engine.

Your not talking 2000 for just 17 seconds which is normal during start, are you? No, of course not. Your talking 2000 rpm idle for anytime the engine is idling.