Replaced the turbo in this car with a JM40 from JM turbo Cooper's. Now somewhere around the 2500rpm range I get terrible surging which I didn't get from the old turbo. You can hear the the waste gate dumping in quick intervals and rpm doesn't change. I backed the waste gate off a tad thinking the ecu thought it was overboosting but to no avail. Any of you boys or girls have any ideas?