I was travelling in my van that's Vortec 350 equipped when it threw a major fit 2.5 hrs from home. The engine was missing violently almost like the ignition was cutting off/on. Long story short, I made it off the interstate to an AutoZone, where I rented a scan tool (Innova 3130). The rental is supposed to be like their loaner tool program where you basically buy the tool, use it, then bring it back for a full refund. I'm supposed to be able to return it to any AutoZone. I haven't done that yet, but if that works out it's a great big bargain.
The tool shows codes and live data, in graph form, and can record/play back info. Pretty good tool.
Turned out to be the MAF sensor. Unplugged it and van ran fine.
AutoZone did give me a total refund of my rental fee when I returned the tool. The scanner is very useful for OBD 2 vehicles and "FREE" is hard to beat.