CM871 Idle Fluctuation

[Nilao]

At idle the egr valve will be cracked open to allow egr to enter the intake. This lope at idle is the egr opening and closing which starves the engine for oxygen. I think the delta-p sensor is probably toast and not allowing the ecm to get an accurate reading on the flow through the egr Venturi.

Taking the pipe off between the egr valve and venturi is interrupting the flow of exhaust gas to the intake which allows the engine to run on 100% clean air, thus the lope goes away due to the lack of exhaust gas interfering with combustion.

Just my opinion on why it goes away if you unhook that pipe.