Nissan Repair: engine light on, new tabs, nissan pathfinder

Question
Okay where do I start. I have a 1997 4WD Nissan Pathfinder manual transmission. I got it in 2008 and so far it's been a great car except for the check engine light problem. 2 1/2 years ago my check engine light came on before I was due for an admission test. Got a diagnostic to waive the test so I could get my tabs. My diagnostic came back with codes P0325 and P0505. I did some research into the idle control valve and a lot of pathfinders had the same problem, my mechanic thought that was what it had to be. With the emission waive I was good for 2 years. Of course I waited until the last minute to get it done before I need new tabs Feb 1st. I bought the idle control valve (NEW) online earlier this month. They just installed it today. 3.5 hours later, and $332 in labor it was fixed. No check engine light! I was so relieved! Then one hour later it came on again while my car was idle at the bank drive through. I do not know what to do. Is it the labor? the part? or the code P0325 Knock Sensor, Bank 1? I am thinking it's that, but on the other hand I think it's still the idle control valve. Why would the engine light go off after the repair and come on only when my car was idle? If it was the knock sensor wouldn't the engine light stay on even after the repair, like it has been for 2 1/2 years? I just don't know what else to do with this issue. Beyond frustrating mystery if you ask me.

Answer
Hi Lizzie -

Yes, the Pathfinders are notorious for these CEL (check engine lights). Sometimes, though, they are nuisance lights.

Could you clarify with me whether you had taken the vehicle in to get the code the second time it came on? Or did you do that and the code P0325 came out? I sould like to know what the current code(s) are.

Also, have you tried resetting the light and see if it returns?

Please let me know -
aloha
Calvin