Troubleshooting high load I've got an old MacBook Pro with a Core2Duo CPU that regularly has a load up in the 3s or 4s.

thumper:~ joliver.sa$ sysctl -n hw.ncpu
2
thumper:~ joliver.sa$ uptime
 9:24  up 4 days, 16:31, 3 users, load averages: 3.50 4.09 3.83

Processes: 295 total, 2 running, 14 stuck, 279 sleeping, 1225 threads                                                                                                                                  09:24:43
Load Avg: 3.59, 4.06, 3.83  CPU usage: 4.83% user, 6.28% sys, 88.88% idle  SharedLibs: 17M resident, 20M data, 0B linkedit. MemRegions: 48719 total, 3030M resident, 159M private, 655M shared.
PhysMem: 7200M used (1446M wired), 991M unused. VM: 698G vsize, 1071M framework vsize, 0(0) swapins, 0(0) swapouts. Networks: packets: 38837251/53G in, 7236342/639M out.
Disks: 1045731/15G read, 1170955/228G written.


This clearly isn't a CPU issue.  It doesn't appear to be a memory issue.  Disk IO doesn't seem to be an issue.  Some of the "stuck" processes were things I could kill off, but the load has only gotten worse in the last few minutes.  How else can I find out what's lining up waiting for attention?
Here are some troubleshooting steps:

Run ps aux to see which ones are actually running real time.

Next run the iostat to watch the actual CPU loading and see if you can determine if some new processes are running and whether that is increasing or decreasing the IO and CPU load on the system.

For comparison here is the output of the iostat I have.

disk0           disk1           disk2       cpu     load average
    KB/t tps  MB/s     KB/t tps  MB/s     KB/t tps  MB/s  us sy id   1m   5m   15m
   26.55   3  0.08   177.96   0  0.00    65.01   0  0.00   3  2 96  1.16 0.96 0.90


Some Git and Homebrew are know to create the problem so check your versions to latest update.