1999 service engine soon

The service engine soon light comes on after short drive. The code PO401 means insufficient flow detected. I did the following:

Bought a new EGR and install, resetting error code. After a few days the same error code PO401 comes up again.
Install the original EGR but after cleaning the plunger and outer debris. The error code reset and after few days of driving the same error code PO401 comes on again.
Took the EGR OUT and cleaned the vacuum piping with a wire and installed old EGR again after resetting error code. The problem comes on again with the same error code po401.Some car history prior to this problem. The service light came on and the code was related to the MAF (mass air flow switch) which was replaced.
As soon as the MAF was replaced one day later this PO401 started.

Confused as to whats next. I had terrible Dealer experiences so prefer to fix myself.

Can someone help if you had similar problems.

Thanks..........

Welcome to AF. Did you have the pcv valve replaced or an upper intake manifold done recently?

Welcome to AF. Did you have the pcv valve replaced or an upper intake manifold done recently?
I did have the PCV valve replaced recently. No work done on the intake manifold.

Recheck your pcv installation you may have left out one of the 2 "o" rings. Omission of these seals can set that code especially larger one , easy to forget.

The service engine soon light comes on after short drive. The code PO401 means insufficient flow detected. I did the following:

Bought a new EGR and install, resetting error code. After a few days the same error code PO401 comes up again.
Install the original EGR but after cleaning the plunger and outer debris. The error code reset and after few days of driving the same error code PO401 comes on again.
Took the EGR OUT and cleaned the vacuum piping with a wire and installed old EGR again after resetting error code. The problem comes on again with the same error code po401.Some car history prior to this problem. The service light came on and the code was related to the MAF (mass air flow switch) which was replaced.
As soon as the MAF was replaced one day later this PO401 started.

Confused as to whats next. I had terrible Dealer experiences so prefer to fix myself.

Can someone help if you had similar problems.

Thanks..........

Why did you replace the EGR valve?

Problem solved. (PCV valve I install was removed and original one installed).
The big O ring was in but the PCV installed had no small O ring.

Thanks for asking why I replaced the PCV valve. (When I installed the new MAF sensor I decided to replace a new PCV valve aftermarket for NO reason).

Lesson for me track one problem at a time.

So my original EGR in and the Original PCV in. My only problem was a MAF sensor. My new EGR removed soon after problem code re-occur.

Stock with a new EGR (Price with gasket $245.00)

Excellent site. Thank you so much.........