Indeed, I did.

A few observations after enabling "BAC idle up":

There are two easy inputs to use- AC or P/S...my car has neither and the AC connector was right under the rest of my wiring, so that's the first one I tried.
It works beautifully, idle jumps to @900 RPM when the fan is active.

I then decided to try the P/S input- located at the d/s strut tower, this connector required a jumper wire to access- and it too works, but the idle doesn't rise quite as much and is somewhat uneven.

I'm going to switch back and see if results stay consistent (it's possible my BAC valve is degrading and causing the slight roughness).

It'll be a while before I can say much about this- with the advent of colder weather my fan hasn't come on at all for nearly two months, so it's hard to gather impressions.

 

One of the reasons why you are noticing a more steady idle with the A/C input is because the timing is advanced further at idle than with the P/S input. This is especially helpful on ported engines, which tend to like more idle timing anyway.

So you didn't tap right into the engine harness at pin 1E by the ECU? You hooked it in somewhere under the hood?

 

The simplest way to tap into pin 1E would be at the refrigerant pressure switch or stock e-fan relay (L/O wire on AC and Front harnesses). The front bumper/battery area is perfect for connecting up to an aftermarket fan relay. I've been meaning to tap into this exact wire to enable the BAC idle up with my fan, but haven't had the time yet. Too many other projects at the moment.


S4 FSM page 50-31



S4 FSM page 50-38

 

An underhood pic of these locations would be great for anyone reading this thread (using MS Paint to put a little box around the location in the pic). And as I said, I'm planning on eventually doing a writeup that explains how to use the s4, s5, and probably the Starion thermoswitches.

 

well i was thinking about a write up as well, but never got around to taking pictures. i used a mark VIII two speed fan (wired only one speed), a taurus relay (80amps), an a honda (yes i know) thermo switch from a LS motor (B18b1). the reason i switched to this is because i could not find a cheap 40 amp or higher normally closed relay that would work with the stock thermoswitch. i kno hondas pretty well and my friend had a spare LS lying around so i took the theroswitch, and what do you kno, it fits. its a two prong switch and switches at 204. i also wired it hot so the fan will continue running while the car is off, but i might switch that pretty soon. power to the relay directly from the battery for pin 30. then a seperate wire for the relay pin 85 runs to the thermoswitch first then back to the relay, 86 grounds out, and 87 to the fan motor

 

Typically, you'd see the thermoswitch used on the ground leg of the relay.
Does the same thing with one less wire run between the relay and the switch.

 

any update on this? I have received word that my two-relay method for the s4 thermoswitch works. When I do a writeup I'd like to incorporate A/C idle up and maybe you can handle that part. I think it would be best to show how to do it at the refrigerant pressure switch, because n/a MT cars do not have a factory electric fan relay.

 

Not yet. But I could probably pull my battery this weekend, find the wire and take some pictures. Of course, it sounds like clokker already used this wire on his setup, so you might see if he's got any pictures/info already.

Also, I read back in another thread that Rob_XX_7 found the unused e-fan relay on this MT S4 vert, but it had the wiring looped to nowhere. I'll have to dig around a little on my car to see if the relay, and maybe some usable wiring is actually there.

 

He hasn't hooked up the idle up because he doesn't have a bac for the car yet