The driver was in the passenger seat when a man opened the car door and got inside, demanding she get out as he turned on the ignition.
He then attempted to put cable ties around the woman's hands and threatened her with scissors.
The incident took place on New Street, Bloxwich, at around 2.30pm on Tuesday and resulted in the man fleeing on foot after a passerby heard the woman shouting.
A spokesman for West Midlands Police said: "We’re investigating after a woman was threatened in an attempted carjacking on New Street, Bloxwich, just after 2.30pm on Tuesday.
"The driver in her fifties was in the passenger seat when a man opened the driver’s door and got inside.
"He turned the ignition on and demanded the woman get out of the car.
"He attempted to put cable ties around her hand and threatened her with scissors, causing minor injury.
"Thankfully a member of the public heard her shouting and ran over to help, at which point the man ran off on foot.
"We understand the circumstances of this incident are distressing and want to reassure the community that we are putting every effort into tracing the man responsible."
Anyone with information can contact Live Chat or call 101 quoting the reference number 20/1942475/21.