Partner Crankshaft Sensor Fault

A crankshaft sensor fault could certainly explain those symptoms. The engine control unit (ECU) uses signals from both the crankshaft and camshaft sensors to determine engine position and control ignition and fuel injection timing. A discrepancy in the reference values between these sensors, often due to a faulty crankshaft sensor, can cause significant performance issues. Has the fault code been read? What fault code is stored?

Yeah, the code was something about 'Crankshaft to Camshaft Reference Value' being off. Does that mean I'm right about the crankshaft sensor being the problem?

That fault code strongly suggests an issue with the crankshaft or camshaft position sensor, or the timing between them. While a defective crankshaft sensor is a likely cause, issues with the timing belt itself can also produce similar symptoms. Given the diagnostic code, checking the crankshaft sensor is the logical first step, but I strongly suggest getting it properly diagnosed in a workshop. Misfires can cause severe damage.

Took your advice and brought it to a shop. Turns out the crankshaft sensor was indeed defective. Cost me 340€ to get it sorted. Runs like new again!