Hi to all. I agree with the sender unit being at fault. there seems to be alot of sh*t sender units on the market place. so even if you replace with a new one, be it a colour grey, or black sender unit- two pin ... a lot of patern parts do not match the electrical current rating required to match the temp guage unit/ecu. thus giving you the temp inacuracies. and also no doubt High reving on start up when engine is cold, as i get at the moment with the replacement patern sender along with all the problems that you have described. My original faulty sender unit, gave me high reving on start up, when the engine was warm.. So all i'm waiting for is wam weather, so i will be more enthusiastic to get this problem sorted. As its a right pain of a job to get to the unit out. from the back corner of the engine. ie. fuel filter in the way has to removed to get acess. My advice after my experience is - buy a genuine part- water temp sender ..Thats my next move. best of luck folks