A little more information would be helpful. When does the car hesitate? Driving on the highway? From a stop? When cold? When warmed up? Any maintenance done to the vehicle? Also, would you put the year of your vehicle, along with your trim level in your profile? It helps if we know which engine we're dealing with.
I just had the same problem with my 01 SSEI when i would hit the gas pedal to get up tp speed the car would hesitate and i changed the plugs and wires and it stoped doing it. Like he said check the spark plug wire in the back mine was cracked .
Mine starts hesitating(misfiring) about every 10-20k miles. I just replace the wires. You may need to replace your plugs as well. Also, I have found that sometimes simply using a bottle of fuel system cleaner will resolve the hesitation.
My 2000 had a hesitation problem. I performed a throttle body service and removed and cleaned the fuel injectors. The injectors, in my case, were the cause of the problem. They were really gunked up after 125k on them.
I would recommend checking the plugs for signs of fouling. Make sure your wire heat shields are in place as well.
You might want to take it to a shop that performs the 3-step fuel system service. My shop offers one called Run-Right. Valvoline also makes one. They're very effective.
I have the same question; our 2001 SSEi will start to surge on light acceleration above 35mph. Replaced the spark plugs and wires, no better. (ACDelco parts) Replaced 1 coil, no change. Moved it to each position and never changed. Unplugged the EGR valve, no change. Unplugged the maf, seems to be gone 95% of the time. If it is the maf, why only at part throttle like a secondary miss?