What's the IACV?
*Mine also face the same probs, more feel the irregularities when play around with brake pedal when idling.
Is this related with vacuum hose?
It's an Idle Air Control Valve (IACV) It's the black cyclinder thing you see behind the intake manifold, on the driver side. What it does is control your idle depending on engine load.. however, when you have an air leak (of any sort) the idle will start to vary as the IACV copes with the sudden loss of vaccuum pressure, and compensates, then realises it compensated too much, and lets off too much, and the cycle repeats.
Your brake runs on vaccuum pressure as well, note the black pipe from your brake servo, and notice where it goes. Obviously playing with the brake pedal will result in irregularities, but in most cases, it's a slight rev drop that's not really apparent unless you're looking for it, since it does run with the aid of a vaccuum source as well. That's why with a dead engine, brakes really don't work very well.
A lot of other things run on vaccum as well, and the intake can be said to be the main source of vaccuum. Any of the hoses coming out of this 'source' will result in idle looping, depending on amount, the severity may differ.
But overall, if you have significant rev drop when you use the brakes up to the point that even when you depress it when you're in a complete stop, the engine dies, then it is cause for concern to check if the IACV is doing it's job, or if it's working fine, or pinpoint other source of leaks.
