2000 GT, Need your wisdom

Hey guys, thanks for looking here. I am trying to help a buddy with his 2000 Celica GT that has a 1ZZ-Fe engine and is loosing power. I have not laid eyes on the car yet but asked some standard questions, spark plugs, air filter, timing belt history and such.

He knows where the gas goes in the tank and not much more.

I ordered new plugs, NGK Iridium IX and the air filter that I am sure is hosed. I will clean the throttle body and injectors but can't find any info about the timing belt change intervals. He has no maint. schedule booklet that he can find.

Car has 151K miles and has never had the belts changed so I expect I am working on a real pig at this point. His description while standing over the open hood is no plastic covers on either end, does it have a chain?

I know my SAABs and Hondas but I am way off my beat with Toyos.

Any info on what might cause severe power loss will sure help me here.

Thanks

Gary