Learn Swedish: Om du släpper kopplingen snabbt, så dör motorn. - If you release the clutch quickly, the engine dies.

It acts as a resumptive adverb. When a sentence starts with a subordinate clause like Om du släpper kopplingen snabbt, Swedish often inserts så before the main clause. It functions a bit like 'then' in English ('If you..., then...'), acting as a clear bridge to signal that the main clause is about to start.

Why is the word order dör motorn instead of motorn dör after så?

Because of the V2 (verb-second) rule. The entire 'if' clause along with så counts as the first block of information in the sentence. Therefore, the verb of the main clause (dör) must immediately follow in the second position, before its subject (motorn).

Is it grammatically required to include så here?

No, it is optional. You could perfectly well say Om du släpper kopplingen snabbt, dör motorn. However, using så is extremely common in spoken and informal Swedish, as it makes the transition between the two clauses feel smoother.

Is dör the standard way to say an engine stalls in Swedish?

Yes, saying that an engine 'dies' (motorn dör) is just as common and natural in everyday Swedish as it is in English. You might also encounter the more specific verb tjuvstannar (literally 'thief-stops') used for a car stalling unexpectedly.