96 Altima idle/stall problem

My car has a "bouncing" idle from 0-1500 rpm's at times. It also stalls at redlights and requires throttle to get the engine to start. After replacing both O2 sensors and EGR valve because thats what the codes told us to do the trouble still exists and the CEL is on. It now reads an EGR valve and Knock sensor as the problems. Mechanic is dumbfounded. What else could this be? The problems can occur when the engine is hot or cold but they happen more often after driving for awhile. I've already spent $$$ on two diagnostics. One from Firestone and one from independent mechanic. They both got the same readings. After replacing the parts mentioned it ran fine for 15 minutes. I parked it and no CEL. I went to start it later that evening and it stalled trying to leave my driveway. I parked it and it started right up the next morning only to stall after a 1/2 hour drive and then the CEL came back on. Took it to the mechanic and it spit out the same diagnostic problem as before - EGR valve and Knock sensor. HELP!

Symptoms: the MIL is on. DTC P0400 is stored in the ECM. EGR temperature sensor voltage never falls below 2.0 volts while driving. No vacuum to EGR valve when monitoring with a vacuum gauge.
Field fix: The vacuum port supply for the EGR solenoid was plugged. With the debris cleared, the EGR temp. Sensor voltage would drop below .5 volts while driving.

Try this Gl..

Thanks for the info...I'll relay it to the mechanic on Tues. when I drop the car off again.

FixUrNissan, can you put some of that in "English" so I can explain it to my mechaninc? I'd also like to know what you're talking about.