Signs of bad timing chain tensioner 2005 sentra 1.8 L. Can I replace just tensio

Hello, I really would not "guess" at this, but it is possible depending on your mileage that the tensioner could be faulty, but it could also be that the chain has stretched. Either way, I do not think a lack of power would be a symptom of this, unless timing has already jumped. You may want to get a professional opinion locally to you about this prior to undertaking such a large repair.

https://repairpal.com/timing-chain-noise-may-lead-to-timing-chain-failure-on-higher-mileage-vehicles-010#