Specifically on the ISM, I'd suggest searching and asking on the Cummins under Power Train Garage. The ISM was a long term winner in the Cummins line up. Big enough to put out impressive power, but not as heavy as the Bigger Block ISX. I know that some ISM owner's had EGR related issues, but that was I think around the 2004-2006 era. Other smog changes after that, and I'm not real up on any specific problems related to that year engine. (Suggest you get the sn of the engine, usually can be fund on the info sheet from CC on the bathroom mirror cabinet. Then call Cummins to learn the exact year your engine was built. We have a 2004 model, with a July of 2003 engine.)
On there rest of the coach, normal looking for regular maintenance records, and general overall condition is the normal things to check. Run each system, and when in doubt, have a full PDI performed by a competent person/shop. Check the age of the tires, four digit date code on the tires to do this Week and Year or Year and Week - forget the order).
The Intrigue is a respected model within the CC lineup!
Roo II is our 04 Country Coach Allure 40'
OnDRoad for The JRNY! Enjoy life...