What causes my car to hesitate when going 20 miles an hour?
I would start with the basic tune up first, plugs, wires, cap, rotor, (if newer car you won't have a cap and rotor) air filter, fuel filter. If hesitation persists you can go further like cleaning your Idle Air Control Valve and throttle body. If after you do a tune up, post back with the year, make and model if you're still having issues. Will be easier with more info to go on...........