Is there anyway to check if a Knock Sensor is still good. I think I replaced a knock senor that is still good.

Check the resistance with an ohm meter, I think it is ideal at 5.5 ohms....anyone correct me if I am wrong.

do a SEARCH i remember a thread which tells in detail how to check your KS

check your ECU. If it reads 0304 chances are you need to replace it.

The resistance should be approx 550K Ohms between one terminal and ground (where it attaches to the block).

That should be 550 kohms, or thereabouts. But be aware that a KS can register the correct resistance and still be bad in an intermittent way. Happened to me.

Along with the other suggestions, I'll echo a DBM sentiment - you should be able to do a road test with the knock sensor unplugged.
The negative consequences to this that I can think of (as well as echoing DBM) is you'll get 0304 thrown and in certain circumstances, knocking/pinging could occur which is never good. But if you use premium fuel, the weather isn't too severely hot, and you're not going up steep hills, I think you should be fine for a test drive or two.

Although I'm not sure if anybody has tried this. I'm almost certain that with the KS disconnected, the ECU will not retard the timing at all. I know people have done this on other (new) cars.

The function of the KS is to allow the engine to operate with the most timing advance possible. With the KS disconnected the ECU will default to its most retarded timing setting as a fail-safe mode. Disconnecting the KS has the same effect on the ECU as an inoperative KS, which we know hurts performance.

Rather than just disconnecting the KS, you can connect a 550 kohm resistor in place of the KS to make the ECU think it has a normally operating KS (but also no signals warning the ECU of detonation, please note). I have done this to determine my KS was indeed bad. When the ECU thinks it senses a properly working KS with no detonation signals, then it advances the engine timing up to its maximum setting and you get back all your low end power and smooth acceleration. Just do this as a diagnostic method under light operating conditions - you don't want to continuously run your car like this, for obvious reasons.

OK, I wasn't 100% if the ECU didn't detect any voltage from the KS, if it would drop into fail-safe or simply bypass the KS's functionality and hold timing. I mean, DBM as a primary source, as well as at least one secondary source....but that's why I made it clear I hadn't tried it

A resistor would definitely work to do this kind of test. But like warned, don't forget it's a temporary for-test-purposes replacement