P0300 Mitsubishi - Outlander 2005 Bi/Fuel

Question

Hi, My Mitsubishi Outlander has the code PO300 coming up. The symthons are : chugging /searching engine when cold . When changing to gas, it is perfect. When warm and running on petrol it is also good. I have had other codes come up in the past and have : replaced the plugs, changed the oil/filter etc, changed the throttle acceleration sensor (expensive), and also the MAS sensor. Could this be a fuel / supply problem, and is there an in-line fuel filter ?
Is it getting enough fuel (petrol) and how can I check this, I am totally baffled. Help please - regards Gordon