Just a thought, change the engine coolant tempreture sensor, if it's not already been done. That sensor does two things, Firstly, it tells the gauge in your cluster in the car what the coolant temp is but it's also used more importantly for emmissions and helps with fueling and starting. If the sensor is coloured black it's likely it may be faulty. Change it for a new green one. Normally it'll throw a CEL though but it may be worth a shot.