so the car started throwing a p0400 intermittently. it will stay on for a few
days and then mysteriously dissapear for about a day then come back. i have
disassembled, cleaned and reassembled the egr also replaced the vacuum valve
(circled below) any other suggestions or possible loose wires i should be
looking for?

 

There is a vacuum solenoid under the number 4 intake runner that could be clogged or not working

Look under the dash and find the two green test mode plugs, connect them and turn the key ON. All of the relays and solenoids under the hood will start to click on and off. Put your finger on the EGR vacuum solenoid to see if it clicks. Connect a length of hose to one port and see if you can blow air through the solenoid while it is clicking on and off.

Air should flow then stop in unison with the clicking of the solenoid.

If no air flows the solenoid is clogged and needs to be replaced.

If the solenoid does not click it could be bad, you can check resistance of the solenoid, or look for voltage at the connector while in test more.