I purchased this vehicle around last of August with check engine light on.Carried vehicle to Auto Zone and they told me about EGR, DPSE and solenoid valve. I pulled a vacuum and engine stumbled. Replaced DPSE, reset code with scan tool and light came back on after about 30 miles. Replaced solenoid and reset code with scan tool and light came back on after about 30 miles of driving. No build up on bottom of EGR or inside.
No leaks in vacuum lines that I can find.
Also, engine stumbles when light is OFF but smoothes back out when light comes ON.
Please help??

Sounds like a bad EGR valve.