On My 99 Lexus ES300 i had an issue with the ABS, VSC, check engine light being on and a rough idle, overdrive not engaging, and cruise not working. I brought it in to a mechanic and ever thing seemed fine for a week after they replaced one sensor. I brought it back, the only thing that stayed fixed was the rough idle. They are telling me it is a rear abs/speed sensor. The problem is I do not have the cash to fix right now. So my question is. At what high speeds am I safe driving the lexus without overdrive, and for how long?

Thank for your answers.