I have observed some engines that are very slow up to 70%N1 but normal ablve this
On the 767 CF6 powered aircraft I have experienced tech crews snagging an engine for slow accel only to find out after a HMU/MEC change that the defect remains.
After consultation with GE and time it was discovered that the slow engine was in limits and fast accelerating engine was spooling up to fast which could result in unstable compressor airflow etc etc.
I think a clever upgrade on the ACMS software solved the troubleshooting problems with this defect. (years ago)
Its much easier to pick an engine with different parameters when you have more than one engine to compare with...
