What can cause where you step on the break the speed thermometer goes up n down

If the rpm is going up and down you could have a vacuum leak or a throttle issue. If you are losing vacuum your brake pedal could be harder to push and you could experience a delay in power-assisted braking. If you don't normally work on your own car this will need to be inspected at a shop.Use this link to find a good shop near you. https://repairpal.com/repair-shops Alex