2002 Ford Expedition

The check engine light has never come on, and the only time the surging stops is when I let out of the throttle or when it shifts, other than that the power seems to be ok. I guess it would help if you had a little more info, I have installed a cold air intake and a dynamics tuning chip, if your not familiar with dynamics tuning it is a resister type chip that plugs straight into the mass air connection leaving the wiring for the mass air unconnected, other than that the engine is stock. I bought it used and don't know if it's ever had a tune up, so would worn out spark plugs or coil caps be causing it, or could it be something else?

It didn't do it prior to the chip so maybe the chip is the problem but I don't know, the other day I tested it to see if it would surge any other time than just from a stop and everytime I would step on the throttle to get maximum power it would surge, whether it was from a stop or if I was passing it would surge until it shifted or until I let out of it.