Why does my animation blend with roblox running animation?

I have a Tool called P90 it has an Idle Animation that loops until the P90 is unequipped.

Tool.Equipped:Connect(function ()
    IdleAnim.Looped = true
    IdleAnim:Play()
end)

Tool.Unequipped:Connect(function ()
    IdleAnim:Stop()
end)

In case you are curious here is the link to the animation

Even though the Animation Priority is set to Action4 the default running animation on Roblox overrides my Idle Animation. Link to video

Any Ideas?