Engine hesitation can be a result of low fuel pressure, vacuum leaks, worn or dirty spark plugs or bad spark plug wires. A weak ignition system can lead to misfiring, which can also cause hesitation.
Engine hesitation is usually caused by an air/fuel mixture that is too lean, meaning there is too much air and not enough fuel in the engine. This makes it hard for the spark plugs to create the combustion needed to sufficiently power the engine. This problem may be caused by a bad air flow sensor, a faulty throttle position sensor or poor computer operation. If the vehicle's computer is reading the signal from the air flow sensor incorrectly, it can cause the computer to fail to add enough fuel to the mix, making the mixture lean, and causing hesitation and drag.
It is possible to find out the cause of hesitation by running a few tests. Computer scans can pull fault codes, including misfire codes, and additional tests will help to check fuel pressure and find vacuum leaks. Pulling the spark plugs is another test that is easy and inexpensive to perform, since hesitation can be caused by a spark plug that is dirty or improperly gapped.