Sauber was happier with its latest version of the McLaren-like 'F-duct' system during Friday practice at Sepang.
The Swiss team abandoned the prototype model after practice in Melbourne, and used a modified version aboard the C29 cars in Malaysia.
"We are still too slow," boss Peter Sauber told Blick newspaper, "but at least our rear wing system seems to work."
Technical chief Willy Rampf added: "We sent the data back to Hinwil after practice, where it will be evaluated and then we will decide whether we continue to use it (the F-duct).
"The system is very interesting, but it's only good if it works. Fortunately, we only need ten minutes to put it on and take it off!" he added.
The team's Spanish driver Pedro de la Rosa told EFE news agency: "We are very close to making it work. I am in favour of keeping it (on the car), because the only way to make it work is to test it over more miles."
He added: "It (the system) is much more complex than it seems, even though the concept is very simple.