Tanveer Iqbal's body was found in his Renault Clio in Portland Road, Edgbaston, on Monday afternoon.
The 33-year-old had not been seen since closing his Hi-Tech Music shop in Shireland Road, Smethwick, on Sunday evening and had been reported missing.
Police said his death is currently being treated as suspicious and a post-mortem examination will be carried out.
Mr Iqbal was reported missing at midday on Monday.
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Portland Road was cordoned off between City Road and the Ridgeway and the car has been taken away for investigation.
Det Insp Paul Joyce said police are working "around the clock" to try to piece together Mr Iqbal's last movements.
"Portland Road is likely to remain closed until later today while my team continues to carry out an important forensic examination at the scene," he said.
"I am particularly keen to speak to any witnesses who may have seen Mr Iqbal between closing his shop in Smethwick on Sunday night and the time he was discovered at lunchtime on Monday."

Speaking after talks with his Turkish counterpart in Ankara, the UK prime minister said Islamic State (IS) was a "common enemy" that must be confronted.
He hailed the countries' existing intelligence co-operation and said this would be stepped up further.
The US and EU want Turkey to take a more active role in tackling IS.
At a press conference in the capital, Turkey's prime minister Ahmet Davutoglu said the two countries shared a "strong and common political will" to address the threat posed by foreign fighters travelling to and from conflict zones in Syria and Iraq.
Mr Cameron said that British jihadists had "sometimes" passed through Turkey and the two men had had "productive discussions" over how they could be detained and, if possible, prosecuted.
The UK government is seeking greater powers to confiscate the passports of people returning to the UK from Iraq and Syria who are thought to pose a threat to national security, with Parliament currently debating changes to the law.
Asked whether Turkey could be doing more to identify and stop suspects at its borders, Mr Cameron said the two countries were already working "as closely as we possibly can" to tackle the threat.
He said: "Whether it is about stopping people coming through Turkey to Syria or Iraq to fight for Islamic State, whether it's about making sure we deal with people when they return, whether it is the highest levels of intelligence co-operation that we can possibly achieve between our countries, this is all about making sure people are safer in Turkey and making sure people are safer back home in the UK."
As well as addressing the "extremist ideology" that fuels Islamic State, he reiterated his calls for a transition to a more democratic and representative government in Syria and more efforts towards reconciliation by the new government in Baghdad.
Mr Cameron also hailed a growth in economic links between the UK and Turkey, saying bilateral trade had increased by 60% since 2010.
Making his first visit to Turkey since 2010, Mr Cameron will later be hosted at a dinner by president Recep Tayyip Erdogan.
Mr Cameron will not return to the UK in time for Prime Minister's Questions on Wednesday, with Liberal Democrat Deputy Prime Minister Nick Clegg expected to step in for him.

17 June 2016 Last updated at 18:05 BST
But during a ceremony to honour the victims, one policeman refused the shake hands with the president and his prime minister.
Interviewed on TF1 television afterwards, he said "There are too many problems in the police. We've had enough."
The body of a missing music shop owner has been found in the boot of his car parked in Birmingham.
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David Cameron has said the UK and Turkey are working "hand in glove" to prevent British jihadists returning home after fighting in Iraq and Syria.
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French President Francois Hollande has vowed to improve the protection of police officers, after a police couple was killed by a militant this week.