One problem related to engine belts and pulleys has been reported for the 1999 Toyota 4Runner. The most recently reported issues are listed below.
(1) high pitched engine squeak; assumed worn belt. (2) main pulley key locking main pulley to crank shaft had sheared into two pieces. One piece lost. Pulley moved out of position, stressing belt and causing noise. Remaining piece of the key was embedded and fused into the crank shaft. Pulley key is $ part. Obviously, not durable enough for critical engine part, which when fails can ruin the entire engine. Even 500 x the $ cost would be worth having titanium or tungsten steel part that would never fail. Toyota is cutting corners, sacrificing quality in the name of profit. I risked having to replace the engine -- a $9,000 consideration. (3) fortunately old mill Toyota (omaha, nebraska. Was able to remove the fused part and save the engine. A properly engineered part, even at much greater cost, would have protected me from this risk.