A 23-year-old man from the Tipton area was arrested on Wednesday morning, while a man, aged 21 years old, was arrested in London later that afternoon.
Both will now be questioned by West Midlands Police detectives over the killing of 18-year-old victim Kimani, who was described by his family as "jovial, loving and caring".
He was a passenger in the private hire vehicle when a shotgun was fired at it from a dark hatchback on Dudley Road East.
The car then sped away from the scene of the shooting, which happened just before 1.30am on Sunday, June 20. Three special constables who were nearby came across the scene and tended to the youngster, but nothing could be done to save him.
He was taken to hospital and pronounced dead a short time later.
Detective Inspector Jim Colclough, leading the investigation, said: “These arrests are a significant development, but we are still appealing for people with information to get in touch with us if they have information which could help us.”
Anyone with information is asked to call West Midlands Police on 101, quoting crime number 20/1126386/21. Alternatively, call Crimestoppers anonymously on 0800 555111.