Knock Sensor????

Well, I bought my XJ used one year ago. I made a oil pump change and saw this wires hanging at the left side of the block, I didn't know what it was but the XJ runs fine so I never thought it could be a sensor plug. Anyway, yesturday (After one year running with the sensor unpluged) I was reading the Renix Sensors Catalog and saw this "Knock Sensor". I know what this sensor do. So I went to my XJ and plugged the sensor to see If i can get a better idle because the XJ idles horrible, very irregular. Well I plugged it and I can't feel a change.
What should happen if this sensor is unpluged? What could be the differences I should feel in my engine?, Rough idle or something?

Sorry for the long post, but I'm clueless and need to figure if I change or keep the "Knock Sensor" that I already have.

Thanks

A knock sensor detects knocks in the engine if you can believe that and trys to counteract them by sending the signal to the computer. Your running rough could be caused by a carboned throttle body and or a clogged air filter. Wouldn't hurt to look at all the tune up componants such as spark plugs and wires.

Sean

Already made a tune up. Jeep still has a rough idle.

Knock sensor is there to prevent detonation. When it senses a knock the ECu retards the timing a bit. You can test it by tapping on the block with a hammer while the motor is running, you'll hear the motor change how it's running.
Rought idle is usually an out of spec TPS, a malfunctioning IAC motor or nasty carbond up TB keeping the IAC from doing it's job. You may also have a vacuum leak, but this usually causes a high idle situation, as it's a constant leak.