have you changed the rear tank filter recently?I have seen the return hose from the fuel injector rail get kinked and cause exceesive fuel pressure,and when the car is cold it blubbers and doesn,t want to idle.The engine will idle fine when hot becasue the coolant sensor leans down the fuel mixture enough that the increased fuel pressure doesn't affect the running of the engine.You might blow from the return hose up front and see if there is no restriction going back to the fuel tank,it is a cheap test.