Coulthard, winner of more races than any current driver other than Ferrari's Michael Schumacher, is set to leave McLaren at the end of the season and has listed Toyota and Williams as teams he would like to drive for.
"Ralf, just hurry up and make a decision for God's sake," joked the Scot when asked at a Malaysian Grand Prix news conference whether he would consider a return to Williams, who gave him his debut in 1994.
"It is my intention to be on the grid next year," he added. "And obviously that means finding the most competitive drive that I can."
Williams have one definite vacancy with Colombian Juan Pablo Montoya leaving to join McLaren and it could be two if Ralf fails to agree a contract extension.
That would possibly mean Williams opting for an experienced driver such as Coulthard to partner a rookie talent.
Ralf, the younger brother of Ferrari's six-times world champion, has been linked to Toyota and Renault in the past week although the French manufacturer swiftly denied any negotiations.
"I'm pretty clear about what we want to achieve with Williams this year," said the German, whose contract with the team expires at the end of the season.
"At the moment I am talking to BMW-Williams which is where I am and where I would like to stay. We're still talking about it."
