1990 Beauville with erratic idle once warm

Just purchased a 1990 chevy Beauville with 90K miles on it, 350 V8 TBI, as a dedeicated tow vehicle for a vintage Airstream trailer. Previous owner took care of the van, kept it garaged, and performed regular maintenance. Previously, this van was used to tow their boat btwn PA and Canada a few times a year and that's it--therefore, the low mileage. Anyway, the van starts right up and runs very well-no difficulty with the engine or tranny. The ride is quite smooth. Once it's at operating temp, and I'm stopped at a light or in park and the engine is idling, the idle is very erratic. The engine does not stall, but the idle is not smooth. I plan on getting this looked at--but, I'd like to be armed with some info before I bring it into the shop, as I don't want to be taken over the proverbial coals! What should they be looking for?

Kathy

My first guess would be a vacuum leak.

Check the EGR valve. It could be clogged up. Also as stated above, check your vacuum lines, they get old and brittle.