Hey guys, I've been having a problem for the last couple months and I've been coping with it, think I'll try to solve it again. My question is posted in the topic. S4 N/A. my idle adjust screw used to work, but not anymore. Why? What influences this? It's purely mechanical no?

 

I presume you're referring to the air bleed screw on top of the intake.
It is onle a fine adjustment.

The BAC is the primary idle control.
It assumes the the warmed up engine idle with no load is set my the mechanical linkage stop & the bleed screw.
Then it can compensate for loads (steering, lights, fan, AC, etc.)

There is a complete procedure for idle adjustment in the FSM.

 

The BAC is disconnected. This problem comes in conjunction with a few other mysterious happenings. I.E, My ports are opening with no load on engine.

 

If the auxillary ports are opening when there is no load......then it sounds like the exaust is stopped up a bit since its exaust backpressure that opens them.

If the idle adjustment screw has no effect when the initial set coupler is installed, then it means there is already too much air coming in. As in a vacuum leak or the throttle stop screw has been monkeyed with and the throttle plates are more open than they should be at idle.

 

FWIW, a 1/4 turn of the idle adjust screw should result in a change of about 25 to 50 rpm on a good system with the initial set coupler jumpered. And IIRC, counter-clockwise turns should increase the idle speed, and vice-versa...