does your car have a carburator or is it fuel injected? if it does have a carburator, from what you said, to me it sounds like something is wrong with the automatic choke. it doesnt seem like it would be the ignition becuase then it would make sense that it runs fine after its warmed up but that could be your gas milage problem (i would replaced the spark plugs and see if that helps your mileage). it doenst seem like it would be compression either because, like the ignition, would affect the car all the time not just before it warms up. i just noticed that you mentioned injectors but i dont know if the people that told you knew whether your car was fuel injected or not so check to see which it is and post it. if it isnt the choke, then maybe it is one of the temperature sensors that tell the ecu the car needs more fuel if the engine isnt warmed up. however i am far from an expert, that is just my theory.