Situation:

When the brakes are applied, the car's idle drops/becomes rough (sometimes dies)

Checked:
TPS
BAC
Vac Leaks
Alternator (14.5 V at idle)

Question:
What else should I look for to remedy this situation?
Could the brake booster be at fault? The car idles pretty steady at 750 rpm. It does seem to slightly surge and get rough for about 3 seconds about every 2 minutes or so (kinda like it is in some sort of a cycle contolled by the computer).
Could the removal of the Accelerated Warmup Solinoid (solinoid next to the BAC on top of the UIM) have anything to do with this problem?

 

The AWS solenoid (or Air bypass solenoid) shouldnt have anything to do with this. Its pretty much all BAC. That should compensate for varying loads at idle. I dont know how to test the brake booster..

Well, I just found it. Chapter 11 of the FSM. Starts at page 11-7. FSM can be downloaded at www.fc3s.org

Jarrett

 

Thanks, I'll check it out. Any other ideas anyone??

 

That's a tough one.

You can easily discard the brake booster as your problem by just tapping on the brakes to light up the brake lights, it idle gets rough and drops, it's not the booster. You can also turn on your headlights, if the idle becomes rough, then there's a pb with the idle control, not the brake booster.

here I assume you have series 4, on S5, it's a tad different since the ecu on those has a direct input when the lights are turned on (so, try to max the ventilation instead of the lights).

I would check the voltage at the BAC either at the plug or directly at the ECU to make sure the BAC receives proper signal from ECU. The DC voltage should go down as you turn electrical accessories on (like from 11.5 to 11.0 when you tap on the brakes or turn on the lights). If it checks out ok, then it's something else (I would suspect low engine compression or bad charging system: battery or alt)

Also, make sure your idle speed is set correctly (at 750, with the jumper in as per FSM). Also, make sure you don't have vacuum leaks in the EGR and the ACV by cheking if the diaphragms are holding vacuum.

Hugues -

 

hmmm, I hope I dont run into this problem as Ive removed my BAC.