Regardless what RPM the engine is running, the ECU is expecting a certain flow rate from the injectors - the bigger injectors are firing more fuel in at all revs not just idle - start as you mean to go on, change the easy things first.

Of course, if you don't want my advice (I put a turbocharged RS2000 engine in my old XR4x4 a few years ago so it's safe to say I'm pretty clued up) then don't take it - I couldn't give a cuntyfuck either way