Love those "Check Engine" lights!!!!
Been doing a bit of reading and searching on these EGR issues (P0400).
Purchased the ML from a supremely respected forum member. Check engine light situation was fully disclosed.
EGR tube had been cleaned.
EGR replaced. (I'm guessing new)
Vac lines replaced. (I guess some in back?)

Code would throw usually coasting down from hwy speed say on an exit ramp. It fires more frequently now, with around town driving. No secondary codes.

So today, I dove in.....



Drained and removed overflow tank.


Pulled air filter box lid, MAF assy, and intake ducting to get to the hardly accessible business end. The firewall end......

You can see the EGR tube above. (shiny with a wrinkle section)

I went ahead and pulled it out just to check. Had to be sure it was clean. It was very clean!



Put it all back together. No vac lines in back were undone, before or after.
John H gave me some very good info on Facebook!!
Here is one thing I found up front. First, there is some kind of air pump that I know nothing about!! Lots of vac lines, plumbing, a couple of valves of some kind, and a couple of other components that I haven't as of yet identified.


I did find a vac line to/from the driver's side valve had a hole in it. So I replaced the vac line to this valve.

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John