[Montego]

when was the trans. oil and filter last changed? (if at all) what is the mileage?

 

[Montego]

sometimes the oil gets contaminated with metal particals that confuse the speed sensors, l am not saying that this will cure your problem but it is the next step and well worth a try. use hyundai SP111 fluid and if l remember correctly it takes about seven litres to drain and refill the box but you will not be able to drain the whole system. when you have done this remove the two speed sensors and clean them