Knock Sensor
 

Will a bad knock sensor cause a 95 4Runner 6cyl to lose power?

The check engine light came on in my 95 4Runner and I took it in to see what was wrong and it was the knock sensor. Ever since it came on, the truck has not had any power. When I first start driving down the road, the light will come on and I will notice a loss of power.

How much should it cost to have it replaced?

The knock sensor is under the intake plenum. Probably costly at a shop. The parts are cheap but the labor will cost you. Make sure they replace the pigtail while they're in there.
Oh, and welcome to YT!

yes, it will cause the rig to lose a ton of power. when the sensor detects knocks it will retard the timing until the knocks are no longer detected. aka massive loss of power. it is a huge part of the ECM's setup for controlling teh timing.