If the EGR system is still intact, it could be the EGR valve not closing properly.
 
There is a common problem in a D2 where the hose to the I/C delaminates internally and blocks air flow, although that ususally produces black smoke and doesn't usually affect idle.  Another problem that affects power under load is fuel cut-out due to a failed boost modulator, but once again, not at idle or light throttle.
				
			 
			
		 
			
				
			
			
				MY21.5 L405 D350 Vogue SE with 19s.  Produce LLAMS for LR/RR, Jeep GC/Dodge Ram
VK2HFG and APRS W1 digi, RTK base station using LoRa
			
			
		 
	
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