MAZDA 626 1996 Fool or lower the revolutions

I have a Mazda 626 year 1996 automatic that when placing it in the speed "D" accelerate and suddenly slowed alone, or lower the revolutions and go up immediately and stabilize and so keep doing it, instead if I start it in "S" march wondeeping but it is not the idea since its normal speed is "D" so that it makes all its soft and complete changes. I have been told that it could be the MAF sensor, lower it and clean it but nothing, I want to be sure before changing it since it is quite expensive, I change the cables of spark plugs and spark plugs and the same follows the fault.