Here are a few ideas that might solve your problem:

#1 Oscillator Card, give it a "tune up", you'll need the RC3000 Service Manual and the page that lists the Function Values for the specific model number that you are working on.

#2 The Accelerator Potentiometer might be out of adjustment or it might be worn out and you'll need to replace it.

#3 If the RC that you are working on has a Travel Alarm, it will also have a Travel Inhibit Relay Board that is at the very bottom of the Contactor Panel compartment; remove the metal cover that is behind your legs and find the Relay Board that is at the bottom of same compartment.

If the Inhibit Relay is malfunctioning, then you will need to replace it.