Okay so my civic has a D17A2 engine. The check engine light keeps coming back on saying P0401 (EGR flow insufficient).. Now it seems like an easy fix, just clean out the EGR system, right? Nope... First of all, the cylinder head is completely clean, I just had it machined and everything two months ago. Second, I took the Intake manifold off and the EGR ports were already clean, absolutly no carbon deposits or anything, but I cleaned the ports anyway, and put everything back together. Next, I took the EGR valve off and cleaned it with Carburetor Cleaner. Still the check engine light came on. Here is where it gets weird... I confirmed that the EGR valve itself was work by manually operating it with a jump box, some wire, and alligator clips. When I powered the valve, I could indeed hear it closing and opening, so the EGR valve itself is not the problem.. Then, I cranked the car, and manually opened the EGR valve, and the car did not stall, as it should.. Because the car did not stall when the valve was fully opened, that means there must be a blockage somewhere, but the ports are all clean and the EGR valve is work properly as well. Does anyone have any idea where I could go from here?

 

If you start the engine with the EGR valve removed, it should be sucking air through the port. Maybe you're using the wrong intake gasket or too much (i.e. any) sealing compound on the manifold to head interface and blocking the passages. Also the passage from the exhaust to the valve can get clogged. I'm not sure exactly how the 02 is built it doesn't seem to have the plate on top of the manifold like the older ones do.

 

You have to tune out the system still...