My truck does something odd?

I have a 1992 Toyota pickup 22re two wheel drive it
runs great but it does something weird. It will drive
fine but sometimes when it's going down hills and I
let off the gas and let it roll, the check engine light
will flash on and off a few times. Sometimes I
won't see it happen for weeks and sometimes it
happens for a few days in a row. Anyone know
what it is? 250980 miles on it.