Onan throttle slipping

The throttle cable on my Onan engine was rusty on both ends, making it hard to raise or lower the throttle, so I sprayed the ends with WD-40. Now, every time I set the throttle at a higher RPM, it gradually slips down back to the idle position.

I'm starting to think using WD-40 was a bad move....

Is there anything I can do to fix this?