Your car may fluctuate in idle while applying the brakes due to a problem in the computer. Everything in cars nowadays is regulated by the ECM(Electronic Control Module). A few simple diagnostics tests done by a certified tech can tell you what exactly the problem is. You may also have a bad power brake vacuum booster, this would effect the engine idle when the brakes are applied.
apply your brakes gently while accelerating at the same time
More times than not, it turns out to be the TPS sensor
I HAVE THE SAME VEHICLE AND HAD THE SAME PROBLEM... THERE IS A SERVICE BULLETIN FOR THE IDLE AIR CONTROL VALVE. THAT SOLVED MY INTERMITANT HIGH IDLE.
Check for a vacuum leak
Time for new brakes or adjustment.
possibly
it broke
I would say a vacumn leak. Check hoses, measure vacumn with running at idle and at idle when brakes applied. This assumes you have power brakes and it idles well without the brakes applied. Please make sure that the clutch is working properly... Does your clutch work properly?
The power brake vacuum booster is probably failing.
engine idleing to slow turn up your idle to 1500 rpm at idle drive safe
apply your brakes gently as you accelerate
apply your brakes gently as you accelerate