what does restrictive performance require attention to. my light goes in and out

Sounds like the computer is going into a failure mode, basically it is seeing something it doesn't like. So in order to prevent damage to the engine it is reducing the power output of the engine to allow you to get it to a shop. I would have the shop that did the work reevaluate what they did. Perhaps when they changed the timing tensioner the timing of the engine shifted. Or has another coil pack or the one they replaced is defective. Good luck Clint