stall??

[MEMAGIL at aol.com]

I have an 87 CGT, when i was checking out the car to buy, i opened the oil fill cap while the car was idling and the car nearly stalled.  Is this normal..?? I know the vacuum system is connected to the Evap and opening the oil cap probably disturbs the whole balance of the vacuum pressure...but should it stall out??  Other engines i have had you could open the oil cap without worry of the motor immediatley stalling.