low idle speed

ok, this was aminor problem but has stealy grown worse.
the problem is that my idle speed keeps goign down. When i bought the car for my sister it was idleing at the normal 750 rpm.. Over the course of time it has now sliped down to about 500rpms and when you apply the brakes and stop the idle speed dips down to about 300 and then works it way back to 500rpms. I usually doesent stall but it has once or twice. mainly with excessive breaking when the car isent totaly warm.

i checked the cap and rotor, sparkplugs, wires, and the TBI (i cleaned it out) so now im stumped?

thanks for your help

If it happens when you hit the brakes, I'd say check the line that goes from your intake manifold to your brake booster, make sure the hose isn't cracked and leaking. Next thing, you could have a leaking diaphragm inside of your brake booster. When you (or your sister) hit the brakes, does the pedal feel any different, i.e. harder than normal?

ill check on the hose, i have a 1982 bronco that the brakebooster went out on, however on my sisters daytona the pedel feal fine. thanks

ill check on the hose, i have a 1982 bronco that the brakebooster went out on, however on my sisters daytona the pedel feal fine. thanks

How about the AIS. This sets the amout of air the engine gets at idle. It is located inside the throttle body and is controlled by the SBEC.