Looking for an answer in regards to POSSIBLY a present perfect in a first conditional sentence

My question is about this one sentence which has been driving me crazy. I found a discussion on here about present perfect in a first consditional sentences. "If I’ve…., I’ll be able to, etc.." But my sentence starts with not an "If", but with "When" it goes: "When I’ve saved another 1000 Euros, I’ll be able to buy a car."

I don’t understand how exactly the two tenses here are connected and why can’t we say "When (or once) I save another 1000 Euros, I’ll be able to buy a car"?