car stumbles when electric fan comes on

[red97tj]

my 95 318ic auto has 98k on it right now. i came it electric cooling fan from the factory. well, when the car is idling at a stop light or in park, the car would stumble & shakes bad for a few seconds when the electric fan comes on. the car also slightly stumbles when rolling the car windows all the way up...i guess the car would stumble when there's a surge in current draw.
there's no problems at all with car when i'm driving.
i'm wondering if anyone knows how to solve this problem.
thanks in advance for any feedback.

[gearheadE30]

Make sure that the altermator is in good shape and doesn't have worn bushings. Also check that the belt isn't vibrating. A slight drop in RPM is normal, but it shouldn't be very noticeable.