I cant keep hides my heart alive. The moment i exit the house, he follows me and every resident in chorrol comes running and kills him very quickly before i can leave the city.

Is this the way the quest is supposed to go?

No, it shouldn't go that way. You're supposed to immediately run to the nearest gate, and stay out of the city until he's gone.

You haven't attacked him in any way, have you?

No, but he immediately goes hostile and attacks me after i stab whats-his-name with the langourwine blade. When i leave the house, he follows me and all the residents charge him and kills him in seconds.

If i am invisible, he just stands there while all the residents beat him to death.

The only solution i found was to do the quest at midnight and run to the gate before the guards killed him.

I just noticed that you have a fairly long mod list (in another thread); I wonder if one of those (maybe Reneer's Guard Overhaul?) is affecting the way NPC crimes are detected??

For me he was attacked by some guards but he survived and after hiding behind a house I got the journal update.

That might have been it, i cant remember if NPCs get a free pass to do illegal stuff in the vanilla game.

I just ran really fast out of the front gates. By the time the guard catch up to the Argonian...im gone.

They don't get a free pass, but there may be a difference in how soon the crime is detected. If the guards don't kill him before you get out of the gates, he's safe. That quest is a scripted event; I believe that when you leave the city, he gets removed.

I've done this quest a couple of times (PS3 vanilla) ..I stand behind Mottierre when the Argonian comes in,as soon as he shows I stab Motterre and run out the front door,turn left and jump the fence next to the Mages Guild,sprint behind the Fighters Guild and out the north gate.I head up the hill and into the forest.Wait 24 hrs and then go back thru the south gate to the chapel.Have never had the guards chase the Argonian....Glarrg may be onto something with the mods.

I agree with the run as fast as you can crowd. Listen to their dialogue inside of house, as soon as "OH no, a dark brother hood assasin and a enforcer, what shall I poor M do? (paraphrase) stab M, and run out of the house. Do not give any chance for enforcer to engage with you at all. Simply run all the way out of the city.

I've tried this at a variety of levels and never had a problem. If this doesn't work, (and we have GOTY edition) you have introduced some variable into it, either in mods or your behavior in house.