Ok, the car is started and running. Its a rebuilt S4 TII in a 'vert chassis. I have a BAC valve on the engine, however it is the one off of my old NA engine (the TII one didnt come with the engine, i got a block off plate instead).

I had to modify one of the coolant nipples slightly to get it to fit, but its on there now. The car is currently idling around 1200 rpm, and i'd like to bring that down a bit. The method for turbos is to adjust a screw on the BAC, but since its an NA, it doesnt seem to have that screw (at least not accessably). The screw stop for the throttle return is already backed off fully. Is there a way to adjust the idle valve settings to accomplish the same thing? They seem a bit cryptic, and im not sure what the settings should be for the stock BAC, i dont want to accidentally burn it up or something.

Secondly, the stock tach cuts out and drops to zero when rpms drop below about 900. What could be causing this?

Thanks!

 

I think you could try just zeroing out the dcs for the idle control ... what does it idle at with the bac disconnected?

tach dropping at anywhere from 700-900 is "normal", iirc the rotary trailing code doesn't fire trailing below 800 rpms, so no tach signal.

 

Below about 700 rpms, the ms1 firmware does not fire trailing. To lower the speed using the BAC valve, just decrease the duty cycle at the temperature you're running at (for the warmup-only setting)... I would not recommend using closed-loop idle speed control unless you need it.

Ken

 

Ok, in that case could I signal the tach off of the leading coils (preferably) or off of the tach output pin (less preferably)?

I'll see what it idles at without the BAC plugged in when I get home, but even when the car was fully warmed up, it was sitting at 1100-1200 rpm. Theres no way with the BAC to adjust the normal idle speed (outside of open loop mode)? I may just need to plug up the idle hole in the throttle plate and use the throttle return stop screw

 

You just adjust the duty at the warm-temperature. That's it. no need to do anything else.

Ken

 

topless,

The na throttle body has an idle adjustment screw built in. Use that to adjust the base idle speed with warm engine and bac valve disabled. The std FSM procedure should be fine.

 

Ok, i'll see what playing with the settings there does. I dont have the NA throttle body on it anymore, so that adjustment is out.

 

OK, now I see what you are up to. You'll definitely need to close those throttle plates further. Check to be sure the secondaries are closing completely, and then adjust the primary with the tiny screw on the underside of the throttle body. It's miserable to get at with the TB mounted.

 

yea, i can reach it right behind/underneath the stock TMIC, but right now thats fully backed off. I have the turbo off and am waiting on a rebuild kit for it right now, so i have time to mess with stuff. I'm going to go over all the vac lines again and re-seal stuff as well, and see what i can do with the TB. The shaft that the primary plate was on had been slightly bent when i initially got it, causing it to bind and idle really high, i'll recheck that and how well it sits & seals now.

As of right now, unplugging the BAC or blocking the air hose does nothing, but I def dont think i have the settings correct on it.

 

If the throttle plates have been off the shaft, then they may not have been installed correctly, which will cause some binding as they close as well. Loosen the retaining screws, and let the return spring seat the plate fully closed. Then tighten the screws in that position. Also, be sure to stake or lock those screws. If any one of those falls out, it's a very bad day...

 

If all else fail's u may want to hunt down a s5 primary throttle plate. The primary plate's drilled hole is smaller in a s5 na than a s4 na witch would bring the idle down,
FYI iam not sure if there is a differance or what it is in turbo s4 vs s5 (i don't have a s4 TB to look at)!

 

i've got a spare S4 NA TB with all the various butterflys in it that I may just take a solid plate out of, and drill a small hole myself