some info on sensors

[Skeeg]

i have a 95 240sx SE, and my check engine light is on... i took it to my mechanic to run it on this computer and came up with a few ecu errors.

ones that i remember are, knock sensor, 02 sensor, tps sensor, and possibly one more but i forgot it

1st thing, 02 sensor is bad would my car idle funny or anything? it idles fine and i dont notice anything when driving either.

i think i read that the knock sensor rarely fails and usually is a false error from the 02 sensor being bad?

tps sensor i dont really know haha, right now it seems like a few hundred for the new sensors. but the thing is i dont notice anything wrong with the car running and my gas millage seems fine also.

basically im wondering if there is a way to test the sensors individually by inspection and what to look for as far as that goes, or possibly reading the voltage of the sensor could give me the info?

sorry if this makes no sense, its my 1st 240