Too loose and belt slips causing noise because the pulley can't get a good grip on the pulleys. Too tight and the belt will destroy the bearing inside the accessory that is turning. What is your specific problem? Judging by the age of your Toyota, it's due for some major services. Have you been keeping up on them?
Hello yes i have to agree with Hal and also it may make the battery light come on and the steering will become stiff and any other components on that drive belt system will have bearing problems.HAVE A BLESS DAY from DR.RECO.