Hey ... i have a 93 Marqius and it has a surge problem ..... the car runs great, except when the heater is turned on, it seems like the air conditioning pump is kicking in, on and off when the heater is on to the point it drops the Rpms so low you think the car is going to stall then shuts off and you can litterally hear it speed up to normal idel 10 to 15 seconds later does it again .... any idea on this .... thanks

Is it when the heater is turned on to defrost or all the time?

just when when the heater is on defrost or vents etc..... thanks for asking...

I dont know about vent but if you use the defrost or mix settings the car uses the ac compressor to help clear windows and will cause the engine to surge a little as the clutch is cycling on/off.