2001 6 Cyl Petrol Landcruiser starts, then continually stalls only seconds later as the "Check Engine" light illuminates.

[John Z]

I am a new member to this Forum but have been the owner of a 2001 Toyota GXL 6 Cyl Petrol / LPG Landcruiser for a few years. My recent problem was it started running on a maximum of 5 cylinders. and the following day it will start, idle rough, but die after only a few seconds. If I hold the rpm to say around 3,000 RPM after initial startup, the Check engine light comes on after only 3 or 4 seconds and the engine dies immediately. It will do this whether I am running it on LPG or Petrol. Any suggestions as to what may be the issue? It has plenty of fuel and LPG in the tanks and has not had a recent batch of bad fuel as it has run for a couple of weeks on its existing tank loads. (I don't do may km's..)