Sounds like the Engine Computer lost its memory and has to relearn "minimum throttle" before it will know when it must be in control of idle speed. It also might not give you the normal "idle flare-up" to 1500 rpm when you start the engine. This is the procedure for Chrysler products: Drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals. Try this for your car too. If that doesn't work, ask at the Mazda dealership what must be done to cause the relearn to take place. It's usually not too complicated.