Q: Mazda3 not accelerating

At 200 thousand miles it could be just about anything. You didn’t mention f the Check Engine Light is on, but If it is not on, it probably should be. Turn the key on without starting the engine, the CEL should be on. This is a bulb check feature. If the stays on it means there are trouble codes stored that can help in the diagnosis. These can be read by a technician with the appropriate scan tool. If the check engine light is working, but is not on, this is also a helpful clue because it means the problem will be in a part of the car that is not monitored by the ECU. This is all helpful information to a technician who is performing a diagnosis. You can have that diagnosis done conveniently by contacting YourMechanic. They will send a technician to your home or office to check you acceleration problem and let you know what you need to do next.