Engine bucking/missing after warm up
 

I need some help, I have a 1996 mercury villager and I had noticed that the check engine light was on so I went to autozone and retrieved these codes, 1.po400 Exhaust egr system malfunction
2.po325 knock sensor (ks) faulty signal
3.po420 catalytic converter system efficiency below threshold bank 1.

At the top of the scan document it says:
Code PO400 indicates a fault in the gas recirculation flow for a predetermined period of time.
ok with all that said the van ran fine so honestly I ignored it(I know bad idea) well now it still runs it doesn't stall or anything runs fine down the highway just when the engine is warm and I'm at a complete stop the engine bucks as if trying to move the van forward any ideas here I have looked for broken vacuum lines and none that I see and the egr valve has the diaphragm in it I can reach my hand in and press up and the engine almost stalls .Anybody know what going on here? I tried taking the egr off to clean it but the large tube on the side I cant get it to break. Thanks for reading

Update: got the egr off and cleaned it very well with throttle body cleaner ,with the tube attached no blockage cleaned up nice, diaphram looks fine,still having the same issue

Has anyone had an issue like this or even close to it .Could really use any advice at all. Thanks


Well had 45 people read and no one apparently has had this proplem .Well when I find it I will post it. Replaced plugs that helped but still has this bucking,hessitation. Wish me luck ,I still drive it and the check engine light has yet to come on.

Try to replace the MAF for the hesitation.
For the 3rd code, use spark plug non fouler to bypassing the system. Basically, go to autozone and ask for spark plug non fouler, but make sure you get a right size, and open the the O2 sensor that after the cat after that clear the code. For the knock sensor, there is no way around it. Knocking sensor is a crucial part and can lead to engine failure or breaking the timing chain... Good luck.