90 K Maintenance
The Famous Timing Belt..... newer engine design incorporate the use a toothed belt to keep valve timing in order accomplish the 5 event 4 cycle Otto cycle ( Intake , Compression,ignition, Power , and Exhaust) which makes it possible to transform energy from combustion to mechanical force .
Most Manufacturers recommend replacing it at 90,000 miles in order to avoid serious mechanical damage to valve train in case of timing belt failure .
In some vehicles the water pump is driven by the timing belt and it is recommended to replace at the same time , to assure it will last another 90,000 miles .
Hopefully you have kept up with the 30 and 60k maintenance and it is not necessary to add these services on top of the required schedule.
Common services are :
Timing belt tensioner , pulleys , seals
Valve cover gasket
All checks performed at 30,000 miles