Q: Lexus LS430 Cruise control speed limit

The 2001 LS430 Owner’s Manual refers to an upper limit of 85 MPH in terms of cruise control settings. Apart from that, there is no ECU limit or user-programmable upper speed limit. On some cars, you can program individual keys such that a driver using that pre-programmed key cannot exceed a certain speed in the vehicle. I do not see that customizable feature on your car. What you are describing is clearly a malfunction in the system the exact nature of which would have to be diagnosed. There is a possibility of stored trouble codes but even if no codes are stored there are specific Toyota diagnostic decision trees (in the Factory Service Manual) that are followed to resolve malfunctions of this type. To obtain a diagnostic right at your location, please refer to YourMechanic’s cruise control malfunction diagnostic service request page. If you request that service, the responding certified mechanic will get this diagnosed and resolved, right at your location. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.