I’ve been looking for a solution against the periodic problem of having
aslmanager use a high cpu load. As far as I could read in Google, many people
think that it’s due to a curruption of the aslmanager database.
So here is a solution that was suggested in a forum.
Since my aslmanager process was still running,
I had to kill the process before I started the following steps.

sudo launchctl stop com.apple.syslogd
sudo launchctl stop com.apple.aslmanager
sudo rm /var/log/asl/*
sudo launchctl start com.apple.syslogd

And just to make sure things are uptodate run the maintenance scripts:

sudo periodic daily weekly monthly

It might be that after that when the scheduled aslmanager starts again,
that it run for quite a while and again takes high cou load but this should happen
only once to allow the aslmanager to rebuild it database.
After taht the aslmanager should preiodically run but not use so much cpu for so long.
I’ve just did the steps, so time will tell if that method worked.