MacBook Air slow after waking from sleep The backlight on my MacBook Air broke about a week ago and it fixed by Apple by them replacing the logic board.  Since I've got it back I've had a couple of issues.  Firstly, the machine wouldn't work unless plugged in and the battery wasn't available, I sorted this through resetting the NVRAM and PRAM and that's now working fine.

Secondly, when I wake the computer from sleep it is very slow and the fans come on very loud as well, things like moving the cursor across the screen and jittery and not fluid, likewise opening applications takes forever.  I did manage to open Activity Monitor, I got a CPU system load as 87% and a kernel_task as 310.8% CPU.

Any ideas as to what may be causing it? Or is a fresh install the best option and see if that solves the issues?

Thanks!
Starting in Safe mode should eliminate 3d party applications causing that.

Resetting the SMC should resolve remaining issues with Battery, power ect.

Running Apple Hardware test (twice) to verify no issues there (since the logic board was replaced). Look for RAM issues.

Finally a Console log could tell you who is doing what.