Something like this could be. But i think if the temp sensor is failing the car would behave a bit strange. For example "coldstart" at warm temps which lead to not even starting or overfuel the engine so it starves. (Know this of an ibiza my wife owned) It had a faulty temp sensor and always after short rides (warm engine) it wont start cause the ecu thought its much much colder so injected too much fuel. But maybe the swift uses more than one sensor or even uses other values at start or whatever. Ah and on the ibiza the sensor wastn checked by the ecu so the car wouldnt know if it failed.... Needed months to find this issue.
I still think the swifts problem lays in its Software
Das kann es nicht sein, meiner läuft wenn er kalt ist wie ne eins, wenn er wärmer wird, wird es zunehmend schlechter.