Thanks again for the response!
I have been suspecting the EHA myself, since it seems like the engine don't get the extra fuel it needs when cold. The reason it don't stall unless very cold is probably since idle is set too high. I will try to test the EHA like you described. If the EHA is faulty, will the whole unit need to be raplaced? What will the cost of such an operation be?
By the way, my car does not have a catalytic converter, and thus no O2/lambda-sensor, like the US-models.