Y'all were right.
 

My unexplainable check engine light and rpm fluctuations were due to a dirty EGR valve. It's $50 to replace or I can try to clean it. Is it easy to clean? And if so, what is the best way to go about it? If it's not easy to clean, should I try to install the new one myself, or is it better left to a mechanic? Thanks for the help.

P.S.- Another interesting code came up on the reader. It was an Emission code and the AutoZone folks said it had to do with my gas cap not pressurising correctly? I have a fairly intricate gas cap. Kind of thought this was weird? Any thoughts?

Thanks again.

Glad to hear you got it fixed.:rocker:

Yep, P0455 code will be thrown. The computer will test the pressure in the fuel tank and if the pressure drops rapidly, "P0455 Evaporative Emission Control System Leak Detected (gross leak)"
will be stored in the computer. It happens when you simply forget to click the cap tight. Sometimes you get enough junk on the mouth of the gas filler hole and the rubber gas cap gasket to where air leaks and you can clean both with a damp rag.

The code could have been in history for a while.

Search results for P0401

Sorry I misread. I guess it's not quite fixed yet, but at least now you know the problem. I am guessing they came up with P0401. The EGR is simple enough to remove and clean, but you must also clean the ports to ensure a good circulation. If you replace the EGR, the ports on the engine will still need cleaning. Click above for the posts and you will find a lot of handy cleaning details.

I read in another post on this site that vaccuum hoses within the egr system might be at fault. The authors suggested checking the lines first, and added that the valve itself is rarely the culpret. Can't remember the thread, but do a search and you should find it.

do not buy the valve yet!

the 4.6 is a famous egr SYSTEM clogger. check all of the hoses and clean all the ports and lines then reset the pcm and all should be well.