I believe it's either a 16hp or 17hp on a 48" Exmark TTHP probably 7 years old. The motor surges when at idle, revs up, revs down, up, down. Sometimes dies if the throttle is at it's lowest, but will continue to run any other situation. Engage the PTO, everything runs like a dream. Took it to the shop, they changed out the coils ($200), about a week later, same thing. Took it back, they ran it through test after test and decided that it needs a new carb. This would cost ($500 which includes labor) and they are pretty sure this will fix it. Or, I could replace the motor for $1400 plus a couple hours labor and be assured it is fixed. The other option, which I will NOT be doing is trading it in for $1000 towards a new Turf Tracer or Vantage. I can't pay $7000 cash and WON'T finance that much. Has anyone had the surging motor issue before, how did you fix it and I'd like to hear anyone else's input as well.