So ive got a 2002 3.5...and the wonderful oil in sparkplug tube problem
Ordered a 04 valve cover and gasket from DaveB and installed it yesterday.

**It now idles too high ~1000-1100 rpm and has CEL light on**

I had done the spark plugs before so I was sort of familiar with the whole process. Disconnected all the right connectors and hoses...removed the intake manifold etc etc and finally installed the 04 valve cover and gasket.

I used a bit of permatex sealer in the joint in the valve cover in which the gasket goes, in the sharp corners of the VC.

1.cleaned throttle body
2.reinstalled all my coils
3. reinstalled intake manifold, reinstalled hoses and connectors
4. Installed valve cover
***I dont have a torque wrench, so i hand tightened them, and then gave them another 1/4 spin with a wrench not applying too much force but not leaving loose either
5. put everything else back together

I originally had the little clamps on 2 hoses a bit too high on the egr valve and another hose near the throttle body and gave me a cel light.
I looked around, saw those two clamps too high and thought might be restricting vacuum/air flow. So i moved them down properly.

Did ecu reset, and CEl light was off for ~20 miles although it was idling too high.
Looked under the hood and saw nothing out of the ordinary, no hissing noises either..........??

Now, CEL light is back on with the same high idle!

Maybe the clamps on the hose moved back up with the vibration of the engine.

Gptta start from the small pnvious stuff..

you might want to rent a torque wrench from autozone for jobs like this.. the torque of the IM bolts is important, and that could be causing your idle issues if they're too loose.. aside form that, did you do the idle re-learn procedure?

and there's 2 other procedures that NWP recommends you do after unhooking everything to install the spacers, but i can't remember what they're called...

1.cleaned throttle body

I thought this was a no-no. If you moved the butterfly valve then you made a mistake and this is causing the high idle, It one of those things you should let Nissan do. IIRC

not sure if this will work but...

http://forums.maxima.org/search.php?searchid=323464

Check out all the posts that say they uckfayed up by cleaning the TB.

link doesnt work....but I had cleaned the TB twice before very carefulll and nothign had happened and I dont suspect that as being the problem

I did do the idle air control relearn procedure today and it idlles a lot better now, but my CEL light came back on......guess i gotta get a reader