clutch and brake pedal down car idles funny?

[Typhoonk]

Just looking for some places to look first.

I have a 1992 mx-4 4cycl.
I left my car for about two days without driving it. when I came back my e-brake light was on. Ok, so I checked an topped up my brake fluid.
Now when I stop at a light with the engine warmed up, the clutch pedal in and the brake pedal down, my idle drops to about 350 car shakes and my lights dim.
I take my foot of the brake or the clutch pedal, and my car 'fixes' it's self and runs fine again.
Was thinking it could be air in the system or I need to flush the system out?
kinda curious? the clutch and the brakes use the same fluid right?
just want some sort of idea - cause my brake system is entirely warrentied by speedy so they will fix it for free (it would be faster if I can tell them what is exactly what's happening)

[RoundTop]

if you shift to neutral and remove your foot from the clutch (but still brake) does it happen?

How about on a flat surface, not moving, just clutch no brake.

If so in both these circumstances it could be something with the fuel system or intake sensors. If it only happens with both of them down it is odd as even if there was air in the system it would make it soft and squishy, not lower your RPMs as neither affects the engine.

[LongJohn]

The SOHC is notorious for having idle problems that show up when you change the load. For instance, mine was dying when I pushed in the clutch unless I first gave it a bit of gas. There are many posts about the vent tube going from the valve cover to the intake manifold, and other things regarding this.

Mine got a bit better when I took the big round tube off my TB and squirted some brake cleaner in the idle control valve.

Two things to consider:

1. Why is pushing in the clutch creating enough drag to upset idle? Is your throwout bearing going bad? My problem was in the engine itself -- the thrust bearings were worn out.

2. Why does the change in load upset idle? Mine was a combo of things. People have disconnected the tube from the valve cover to the intake and put a filter to allow blowby (and trap the oil) and had good results. I think that when the car is older, you need to clean up the idle air control and many other things. For instance, during my BP swap I found many bad grounds where I needed to sand the terminals to make them shiny again.

[Ateana]

master and slave cylinder would be my first guess.