Every once in a while my trooper ( fuel injected 2002 ) will rough idle when stopped or in park then engin stalls. It restarts right away but then stalls again. It stays running after several attempts at restart when revved to 2500 - 3000 rpm for a few seconds therafter. I've had tune up - belts, o2 sensor, plugs, oil, and fuel / air filter changed but problem persist. What should I try next?