Heat olive oil in a wide, heavy pot over medium heat.
Add the chorizo and cook for 4 to 5 minutes until the chorizo is lightly browned and slightly crisp.Use a slotted spoon to transfer the chorizo to a bowl. Set aside.
Add the garlic and onions to the pot and cook for 4 to 5 minutes until the onions are soft and golden brown. Use a slotted spoon to remove onions and garlic to the bowl with the chorizo.
Spoon off all but 1 Tbsp. of the oil from the pot.
Add the tomatoes (and their juice) and the chili flakes. Cook on medium high heat for 8 to 10 minutes until the liquid is reduced and the tomatoes are slightly caramelized.
Add the clam juice, saffron, vinegar, sugar and salt. Cover and simmer for 10 minutes to blend the flavors.
Add the clams to the pot and cover. Cook for 5 to 7 minutes until the clams open.
Remove any unopened clams.
Stir in the reserved chorizo, onions and garlic.
Transfer to a bowl, sprinkle with parsley and serve.