I'm having a bit of an idle issue. I put an 800 cca Optima in the car and it seemed to help quite a bit, but not completely fixed.


The car will idle just fine with no loads on. No dips while reving. Before the new battery was put in the car would die when you'd kick any electrical load on (or at least drop to 200 RPM and chug back up). After the new battery was installed it still drops, but only down to maybe 400 RPM. Before the new battery turing the AC on would immediately stall the engine. After the new battery when you kick the AC on it pops up a couple hundred RPM, normal for the most part. Power steering makes it raise up 50 RPM or so now, normal. So the BAC is working...

I've read something about an electrical load sensor or E/L located in the driver side foot well? I don't know what it looks like on the s5, I've owned many s4s and I don't recall much being down there.

Where is it and what does it look like? Is it built into the little black CPU that controls the horn etc?

 

The BAC is the unit that compensates for electrical draw.
It's located on the intake tract and adds air to the intake to raise idle when a large draw is detected.

AFAIK, there is no such thing as an "electrical draw detector", the ECU drives the BAC.

 

Here's the short answer. The FD had a separate electrical load detection computer, and it was located in the passengar side kick panel area near the ECU. The s5 FC had an electrical load detection function, but all the wires went right to the ECU.





The reason why you or somebody else may be confused is because Mazda used a lot of the same idle control terminology across series even as the systems were evolving. In the series 3 GSL-SE and the series 4 turbo cars, idle speed was controlled by the Bypass Air Control valve for small amounts of air (vacuum diaphragm on series 3, electronic duty controlled solenoid on series 4). The Air Supply Valve added additional air mostly under P/S load and this solenoid was not duty controlled. And I am not even talking about the accelerated warmup system because that was only on USDM cars anyway.

On the series 5 the Air Supply Valve was eliminated from both turbo and non turbo models. The duty controlled BAC valve remained, but the service manual labels it as part of what's called the "ISC" or Idle Speed Control system. In the series 6, the term "Idle Speed Control" system is still used, and now the BAC valve is called the ISC valve or idle air control valve. The ISC valve was relocated from the primary runners on the series 5 turbo cars to the back of the plenum chamber on the series 6. The ISC valve in the series 6 took on an additonal role, replacing the anti-afterburn valve in the ACV. Confused yet?

 

I am.

 

Like ARGH says, its a function of the ECU on a series five as his attachments show. I'd suspect the thread owner has a problem with his BAC. Either the wiring/plug on the BAC is bad or the transistor inside the ECU that pulses the BAC is burnt up.

 

Or the alternator may not be providing enough current? That would be the most obvious conclusion. I would run a few tests on the alt to be sure. Attach an ammeter (in series) at the alternator output wire.

Check the voltage of the system with the car running...you should know should be 14.3-14.7 volts.

Also check the Rectifier Diodes by setting your DMM to AC volts, put across the battery. If you get a reading at all your diodes are bad. They are used to convert the AC from the alternator to DC for automotive uses. Now if I can remember the AC can cause interference which may induce a voltage signal into the BAC I mean they are pretty close..I can't remember but I think I remember seeing a tin foil like "shielding" its called around the wires for the BAC. This is to prevent magnetic induction..if its not there or if I'm talking out my *** I can't quite remember...wrap the wiring in tin foil tightly and put electrical tape over top. That may solve the issue.

In case you don't know Induction is the process of charging a conductor from a magnet. The permanent magnets in the alternator produce a ton of magnetic flux which is probably in range of the BAC.

If I'm wrong somebody please correct me but I swear to god I remember shielding around the BAC wires..

 

The BAC works because PS and AC both kick the idle up. Lights make it dip down. The bigger battery helped a lot. I may just buy a new alternator as mine is putting out 13.6 volts at idle and 13.92 peak while revving to 3k.

 

Yeah your alt is shot dude its supposed to be 14.3-14.7 volts.