Technical Fiat Bravo HGT hard start

[VANZETO]

Hello guys I need some help with a problem which maybe someone has had previously. So my Fiat when cold starts perfectly, but after 30 seconds the rpm will drop down to 500 for 2-3 seconds and then go back to 1200 and when the engine is warm it cranks a lot and barely starts like it's choking itself. I don't have any error codes and I've replaced the crankshaft sensor, temperature sensor.

 

[Ven205]

Perhaps an engine rebuild is required? XD