Not a 306 but 307

[Mole man]

Well as title says my misses just bought a 307 hdi xsi with the 136 bhp engine all seemed fine till today when the engine seems to judder when your driving at a constant speed as if you are touching the brakes and then letting of again plus lots of black smoke when you accelerate, anyone have any advice? Or ideas? Been a long time since iv owned a peugeot hdi engine lol