Cold start problem

I have a 2.2 Renault fuel inj. Engine in my small motor home. Engine will start as soon as I turn the key but only runs for 3 to 5 seconds and stalls. Will continue to do this each time I try starting. If by pumping the acc. Fast enough I can get it to keep runining for one to two minutes at a hight RPM it will continue to run normal. If I shut it off and try again in half hour I have the same problem starting it again.