Peugeot 306 TD injector?

Hello, good afternoon. I have a 1995 Peugeot 306 1.9td and when I start it, it jerks a lot and emits a lot of bluish-white smoke that smells like diesel. Could it be that an injector has failed? (The engine code is D8A.) The idle is unstable, as if diesel isn't getting into one cylinder. I hope you can help me. Thank you.

It's generally a symptom of a bad injector; you can remove and clean them, then have them checked. It could also be the fuel pump, but you always start with the injectors. Is the exhaust sound intermittent?

The exhaust sound is constant, but the idle seems as if a cylinder is not exploding, it's like a ta ta ta (silence) ta ta ta ta ta ta ta (silence)

I suspected it from the beginning, hahaha. It measures compression, but it could be an injector, as you rightly say. But does the black smoke appear when you're driving or only when starting?

No, it's blue and white and smells like Gasoil