96 Camaro P0400 code, cannot figure out how to fix. HELP.
 

I bought a 96 z28 like 4 months ago and I've always had a p0400 code. I replaced the EGR, the EGR solenoid, and tested the pigtail to the solenoid and got 12 vdc and ohmed it out and got proper readings. I didn't know what to do after that so I took it to a shop, and had them look at it and they ran a vacuum test, replaced a vacuum line and the code was gone. 100 miles later it comes back same code. This is where it becomes weird. I was driving down the high way and hit a huge pothole and within 20 feet of doing so my check engine light went out. And now it has come back, and I've manually opened the egr and did that test to see if the pathways were clogged, and they weren't. So I have no idea what to do. Please help my devil car.

check connector to the egr. sometimes the contacts get lose and need to be bent back in shape to get good contact.