I have a 2000 ford ranger with 220K When i come to a stop (sometmes) the voltage meter drops and the oil guage starts to flutter. Truck runs fine no noise or wanting to stall. as i rev it guage goes up and oil guage stops moving. Had altinator checked its fine. Belt does not slip. battery fairly new.
The older a vehicle gets, it tends to do some things that are unexplainable. The guages may be a little screwy themselves. If they both started doing it at the same time, most likely it is the guage that is off. Dont worry about it, if the engine starts making noises or the battery doesnt seem to be working the way it should, then that is when you have a problem. Right now, my theory is that the guages are just screwy. What about the fuel guage? Does this seem to float also when accelerating or slowing down? This is a Ford thing. Most of them do it.
the fule guage does not read right at 1/4 tank. I ran out of gas one time thinking I still had at leat an 1/8 of a tank left