Fun going by horse or stolen car (9)

I believe the answer is:

joyriding

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'horse or stolen car' is the definition.
I can't judge whether this definition defines the answer.

'fun going' is the wordplay.
'fun' becomes 'joy' (I can't justify this - if you can you should believe this answer much more).
'going' becomes 'riding' (riding is a kind of going).
'joy'+'riding'='JOYRIDING'

'by' is the link.

Can you help me to learn more?

(Another definition for joyriding that I've seen is " "Sport" of car thieves".)

I've seen this clue in The Daily Express.

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