I just purchased a 91 b2200 158,000 miles, when cold she fires rite up and drives just fine and temp stays perfect. Pull up to the market ten minutes later get in and start it, fires rite up, idles rough and stops running. Start it again, idles rough and clears out and runs and drives fine. I changed plugs, cap, rotor, changed the oil and filter and still has the same problem. Fuel injected so i know its not a carburetor issue. Any suggestions ? Thanks

 

Scan for fault codes.

Does it use / loose coolant.

Check fuel pressure & fuel flow.