Strange knock and misfire at idle after EGR cleaning

Hello, first post here, seeking help with an at first intermittent MAF sensor code that has now progressed to rattling at idle that sounds like motor knock.

Here's a list of everything that has been replaced since I purchased the car about a month ago.
-EGR cooler, valve, connecting pipe and intake manifold cleaned with a pressure washer and nylon brushes.
-2 week period where everything ran fine
Car throws code for MAF sensor (po101 and P0171)
-Cleaned MAF sensor, issue resolved for about a week after, then same codes displayed.
-Replaced MAF sensor at this point (OEM DENSO replacement)
-Replace spark plugs
-After 2 weeks (last Friday) car started rattling really badly when coming to a stop (gasoline engine turning off) but drove smoothly on the highway.

Here's everything I have attempted to do to fix the poor idle in the last few days:
-Switch cylinder 2 coil pack to cylinder 4, no change in idle.
-Clean fuel injectors, no change.
-Add oil catch can, clean pool of oil in intake, no change.
-Replace MAF for a second time (duralast), no change

The only "smoking gun" I have is short term fuel trim values being +20%, I am afraid to idle the car longer to do O2 sensor diagnosis due to the bad knock. If there is any other scan tool information that would help with solving the problem, please let me know, I have a scanner

Car is currently displaying the following codes: P0302 (cylinder 2 misfire) P0171 (system too lean) po101 (mass air flow sensor range bad)
I am not burning coolant, have put 3000 miles on the odometer since buying it with no coolant consumption. After cleaning the intake manifold for the first time, I had no cold start rattles for 2 weeks.

Consumes about 1/2 a quart of oil between oil changes but this may just be oil pooling in the intake because of the PCV design, I just installed a catch can and will have to wait to see results.

Any help would be appreciated, I am thinking there might be a vacuum leak or EGR gaskets leaking, but I haven't seen much information on this happening to others which leads me to believe it might be something else. If anyone has a vacuum diagram or common leak points to check, that would be helpful as well.

 

209k. I can't tell if the head gasket has been replaced in the past. I will try some of the suggestions in the replies and update with any changes later tonight.

 

I'm an idiot left the EGR valve unbolted from the housing (or the bolts worked their way loose, I didn't use any threadlocker, will be doing that upon reassembly), I'm surprised it lasted this long without acting up. I unhooked the valve connector and the car ran fine, will be heading to the junkyard tomorrow to get new bolts.

 

Got it all put back together with the new bolts from the junkyard and loctite red, everything runs great after a 50 mile drive and I'm getting about 3mpg more than before because of the injector cleaning. My biggest tip for getting that bolt on the close side of the motor is to use a 10mm socket on a 1/4 socket drive to 1/4 hex drive adapter and driving the 1/4 hex end with a 1/4 socket. The skinny shaft should clear the various coolant lines with only the EGR cooler to manifold pipe removed and the 1 12mm nut and e-torx stud removed.

 

The lower 10mm bolts (not the black plastic hex ones) were missing on mine, whether they somehow loosened and dropped or were never reinstalled is a mystery to me. The threads are on the EGR valve side and the bolts come up through the elbow with the e-torx stud from the bottom