There is no throttle cable adjustment. If the cable is properly install, and if you have the correct one, everything should be ok. Unplug the cable from the throttle and the gas pedal and try moving it back and forth, maybe the cable is seizing.
You can't adjust the pressure plate pressure, the only thing you can adjust is the clutch pedal travel. Check at the base tof the clutch pedal, you will see a stopping screw, that's the adjustment screw. But i'm not sure that will solve your problem. You should check if your clutch is slipping.
Nic.
