Rolling start RPM glitch - Free Play only

When cars are off to a rolling start during the NASCAR career races, everything seems okay - the cars are steadily humming along right before the green light.

However, select rolling starts before a Free Play race, and the car’s revs are bouncing every few seconds. Not on the redline but just stuttering up and down every few seconds. Quite annoying. A fix would be nice.

Thank you!

An observation: the driver taps on the brakes every two seconds and drives in a slight zig-zag pattern before the counter hits zero.