Good evening to the brain trust.
I have cruise control up to an including 29 mph and none 30 and there after. Any ideas?

Thanks

What is the history of the car?

Is it a USA market car?

This has drive by wire so there isn't a CC actuator.

What happens when you set the speed at say 25 , let it stabilize then press the accelerate / up speed button?

Thanks for your assistance. USA model. When I set at 25 cruise sets. Use the lever to accelerate to 29 still good. accelerate to 30 and above failure

Got a scan tool? I wonder if the wheel speed sensors are erratic the faster you go and the CC drops out as a safety. The other systems might not drop out if they have different error code limits.

I think uneven tire diameter might do that. Do you get a warning light on the dash for ASR or anything?

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

mismatched tires come to mind. SHOULD be same brand and size. must also be CORRECT size as installed when new. not all brands are the same diameter with the same size. good luck, chuck.