'93 Blazer...check engine light on

Now, before you call me an idiot read the whole thing.

I just got a '93 S-10 Blazer from the estate of a deceased friend. I know minor problems that need to be worked on but one i just found out today.\

When i stop for a short period of time (usually about 30 seconds of idleing) the "service engine soon" light comes on. When i begin to drive again, the light goes off.

I know about 3-4 years ago he replaced the motor with a remanufactured one. It's the Vortec 4.3 fuel injection.

I don't know much about s-10 Blazers, i'm more of a Bronco guy. I just picked this up as a beater to use while i work on my two Broncos. I don't want this to cause a a huge problem, so i'm addressing it now.

Any help? Thanks!

Something that drops when low rpm and rises with higher rpm, like oil pressure, vacuum ?

could be a number of different things, go someplace and get the code read, if the light isn't on when read, it should still be in the failure history records. i believe places like tires plus do code reading for free, but don't let them replace or fix anything, the'll just shotgun a part in and call it good enough haha