***Hi All My Misses Has Just Bought A 307 Hdi Xsi All Was Good For A Few Days Then Travelling At Constant Speed It Starts To Judder and surge And A Lot Of Black Smoke! ***We had it on diagnostics and the only fault which came up was the coolant***solenoid***bypass valve P1598, would this cause the symptoms I'm explaining? Also looked at new thermostat housings and they don't have any where for the***coolant temp sensor***to plug into? If anyone could help that would be great! I'm not used to these modern peugeot iv got a 306***gti***6***and is so much simpler compared to this any help would be much apreciated!