new engine codes for me

my 01 passport has been acting up lately. flashing cel when accelerating, and now it is on solid. I have the folloing codes po300, po401 and po404. I did the plugs about 40000 ago and did the intake gasket and egr cleaning last summer. here are the symptoms. when starting after it sits for a more than 4-5 hours,,,,starts, dies sometimes, idles really rough. After that it runs fine. when turning it off sometimes, the throttle revs and lowers on its own. up to about 2700 rps then down repeatedly. It runs fine in between those times. Is it time for new plugs again already and an egr clean again?

I'm thinking leaky intake manifold gaskets.

The flashing CEL means there is a catalyst damaging misfire. It flashes to communicate a sense of urgency. It's important that you don't drive it like that.

2x for leaking intake manifold gasket. see the faq link below for details.

i sprayed some starting fluid around the intake while it was running and it didnt change the way it ran, also i can not hear any vacuum at this point. I have been driving it for some time, unfortunately i dont have a choice, it seems to run fine while driving. Now the cel is just on solid. I will check the img again this weekend. i hope it is not that again, just did it last summer, i think...or maybe the summer before.

Do you remember what kind of plugs you put in?

i put in the denso's. i will do the egr clean this coming week to see if that helps.

Yeah diagnostics can be so tough with these,my shop manual uses a tech2 scanner for all flow charts.I did not have $3000.00 to get one and then the program card.
I have had those codes in 'o1 3.2L Rodeo sport,I had changed the o2 sensors,nothing then cat converters.I think you may be in that area but it was a while ago.
Intake Man gasket I did twice 129,000 miles on it now,the bakelite spacer cracks and is tough to spot,the starting fluid was a good idea imho,I really wish there was another method to chase problems w/out the tech 2.
I am in a mess with codesP1515,P1125and P1295 along with reduced power lt and it looks like I am alone,here.
I will post my solution when it happpens,sooner the better.
Good luck SF
Fuel pressure regulator will give some crazy codes as well,test the fuel rail pressure.When it went bad it drove the pcm crazy!