No or little throttle response in R

[Kris12]

Having an issue with reverse gear, when the transmission is in R, the car goes backwards slowly when I let go of the brake pedal. So far so good. But when I try to accelerate backwards or go uphill, theres no throttle response and the car stops if Im going uphill. I was recently stationary with the car in reverse and the throttle to the floor. No revving or anything, just above 1000 rpm. If I get the revs up, its ok and it accelerates.

Anybody knows why this happens, or what part could cause the problem?

[Guest 2]

Get a fault code scan done on the car.