It's hard to push gas pedal after stop.

I have Toyota Camry CE 2000. It’s hard to PUSH gas pedal after I make a STOP. While I’m driving, even very slow (even 1 m/h) I don’t have such problem. Also, when it happens if I shut of engine and start it again problem disappears for a while, then it happens again. I cleaned throttle but it did not help. Please help.