This is my understanding. OOに来た時： 1. When one came OO (le temps passé) <common usage> 2. When one come OO (l'hypothèse du temps "présent") You don't know 1 or 2 until reading succesive phrase"車でOOに会いに行くよ". OOに来る時： 1. When one will come OO (l'hypothèse du temps "futur") Comparing two expressions, OOに来た時 is often used if the plan is already fixed, and OOに来る時 is often used if the plan is not concretely fixed.

"来た時、会いに行く" means that someone is coming "来る時、会いに行く" means that someone will come in the future

来た時 = the time after she came 来る時 = the before and until she came

Personellement, je ne dirais jamais, "Eleysが奈良に来た時、車でOOに会いに行くよ。", qui me semble un peu bizarre car en général, on ne peut pas utiliser le passé ainsi que le présent ou le future dans une phrase.

Both sentences are correct and can mean the same situation, but the mental position is different. In the first phrase, the speaker is imaging the situation that Eleys has arrived at Nara someday in the future and he is speaking from that point of time. So Eleys "has already come", and he is going to see her by car. In the second phrase, the speaker's consciousness remains at the present time. In this case, Eleys may come "in the future", then he will pick her up.