1996 Geo Tracker

No. A knock sensor will just alert your vehicle's computer that it is knocking and if you do not recieve a check engine light when it knocks, your sensor may be bad but, a bad sensor will not create a knocking noise only sense it (hence the word "sensor" for sensing). a knock from the block (deep in the engine) can be a bad thing as it may be indicating a bad main rod. The Rod is what your pistons are hooked to. When the pistons are running, they turn the rod in a circle whick transfers to the front pulley to turn the belts and the the rear that provides the power to your transmission to turn your wheels (in so many words). you really should have this taken a look at by a compitent mechanic (i say compitent because i have run into too many incompitent ones at garages who call themselves mechanics when all they really know is what a Tire & Lube Mechanic knows LOL). Be safe.

Okay thanks. I wasn't sure that's why I asked. I already have another motor that is good. I will just change them out and rebuild the other one if it can be.

A knock sensor will not cause a knock at an idle. Its purpose is to adjust timing to the perfect point right before engine knock begins.