po402 and po171 codes

2000 f-150 4.2 v6 engine. Appx two months ago I changed the egr valve after getting a po 402 (exessive flow) code. The truck ran OK but lately it has run poorley. It sometimes hesitates or misses. I checked the plugs and wires...all is well.
Any Ideas! Thanks!

P0402 - Clean both the EGR valve, and all the egr vaccum passages.
P0171 - Lean code, the egr valve stuck open, or bad egr gasket.

How bad was the orginal EGR valve?

I saved the old egr valve and just examined it. It appears to be fouled with soot or black dust (carbon). Could I have reused it if I cleaned it out. Too late now, I already installed a new one!
I will check all the hoses coming off the egr valve as you suggested. I guess I could remove the new egr to check the gasket, I installed it dry---no gasket cement used.
On another site I,m told the dpse senser goes bad---should I change it also?

Thanks

Check the vacuum passages from the EGR port going into your intake.

Clean the mating surface of EGR and Intake, use a dry gasket.
The unmetered air leaks from no gasket, was probably causing your codes.

This OBD II code refers to the EGR valve circuit and the usual culprit is a blocked egr passage. Since the EGR passage is restricted, the ECM tries to compensate for the flow which results in an "excesssive flow code"

This is fixed by removing the EGR valve, EGR tube, throttle body and sometimes the upper intake manifold. To clean you need carburetor spray, thin brake wire cable and and a compressed air blower.

Most of the time the blockage is in the throttle body. Don't worry about the DPFE.

Well...here goes!
I was going to remove the egr valve today and start from scratch, that's when I found a pvc tube that came from the right valve cover just hanging there. I found where it was supposed to be connected and got to thinking. Could something as simple as this be the cause of my problems. I ran the engine and sprayed the vacumn hoses and egr gasket with no negative results. I had mentioned earlier that I had put the gasket on dry...meaning that I used no adhesive on the gasket..not no gasket at all. There is only one vacumn line coming off the egr valve and it looked good. I also cleaned the maf sensor and changed the air filter. Anyway
I had the engie codes reset...no check engine light on now...for how long I don't know!
Drove about 20 miles today and not a hint of hesitation, pre-ignitiion, missing or anything else. So far so good.
I know it,s a long shot---if the problem comes back I,ll do as you suggested.
Thanks!

90% of unmetered air leaks are usually caused by a bad EGR, or PCV system.
Even though the PCV system is fixed, it's still possible for air to sneak in between the egr valve and the intake manifold.

Ford 4.2 doesnt have a "true" PCV valve. Its built in.

Most common cause of this code in Fords is dirty MAF sensor. Especially if you have a K&N filter.

Next is defective intake manifold gaskets which leaks when its cold outside. Ford has a TSB on this defect.

Next try O2 sensors.

EGR code is in the PO400 range

How about an EGR regulator malfunction?