97 Rough Idle

97 EB w/5.4ltr
Engine idles rough, on several occasions it has cut off, but will start again with no problem. Stoped by Advance Auto, according to the behind the counter guy, I have 2 bad 02 sensers, one up stream and one down stream, short harness and long harness.. When I asked what does this mean, he could not answer, only told me that I need to purchase both, so I did. $112.00
Where are these sensers located and, is there a sequence in the replacment proecess. The vehicle only has 90,000 miles and I have been through this several times along with coil replacement. In the past, I have let several, not so dependable mechanics, make the repairs. I dont trust them anymore and want to try the repair myself.
Any help would be greatly appreciated.
 

Just installed both new C02 sensers and no improvement.
Still idles rough, seems to worse after the engine gets warm.
Any ideas?

The fastest easiest route is to go to a dealer and hook it up to a diagnostic machine, ( 119$ at my trip to one last month) They guaranteed they would find the problem even w/o a code. Thats just to hook it up. They did mine in under 30 minutes, total of $180 labor and $94 for a coil, (ouch). But yours may not be a coil, and could go out and spend a few bucks on filters because you're due for them anyways.

Thanks for the input.
I just replaced all 4 O2 censers. Still no change in idle, in fact, it is getting worse and even cutting off when stopping.
I rechecked the trouble code and, the problem now reads as air/fuel too lean. The exhaust smells like thruster starter fluid.
I am lost for ideas, I do not want to take it to a ripoff shop.
Any ideas?

Checkfor any unmetered air entering the intake,  the PCV hose at the back of the manifold for cracks.. Could be MAF..

Thanks,
 
I can hear a hissing sound from the top of motor. I removed the plastic sheild to expose the throtle body, but could not locate the sound.