I have a 99 Honda accord EX 2.3L engine and was getting a code P401. This of course is showing the EGR valve has insufficient flow. I took off the EGR valve and cleaned the best I could, but the code kept coming back. Also the car stalled from time to time out of nowhere and then would run fine for days. The throttle did not hesitate when this was happening but the code kept coming back.

Today I saw this YouTube video: and decided to open my upper "Air Intake Plenum" to clean the EGR port area. Sure enough the EGR valve port was totally blocked up with carbon. I cleaned out the port (and top of the port opening) then blew it out through the EGR hole with a reverse vacuum. This worked because carbon shot out the open end of the EGR port of the air intake. I did spray the top of the air intake with throttle body cleaner and then put the car back together. Now the car surges during idle. No codes pop up.

When I unplug the IAC Valve and start it up, it is surging again. Don't know if opening my vacuum lines caused this because; had to remove the vacuum line on the bottom of the IAC valve (among others) and I heard it hiss as to relieve some pressure while disassembling.

I assume I put the EGR valve back on the right way because the connector on the EGR valve was facing the same way as the loose connector of the wire coming in (from the right side of the engine). I mention this because I did not actually look at the bottom of the EGR valve before putting it in. I just assume I have it right.

Anyway, when the EGR port was gunked up bad with no surging just popping up the P401 code and occasional stall during slow down, but now that I cleaned out the EGR port via the Throttle Body Air Intake Plenum the car is surging during idle. It looks like I reconnected everything. The thing that sucks is I need this car for a trip in a few days. Ouch. Where should I look?

 

Did you reset the ECU after cleaning it? ie. Unhook the battery for 30sec, reconnect it, start the engine, hold throttle @3000rpm until engine is up to temp (first fan cycle), shut the car off, and then proceed with normal operation? If not, try that first and see if that sorts it out and then update the thread. GL

edit: Also double check all the connections make sure you don't have a vacuum leak anywhere. Spay some carb fluid, or brakleen around all the vacuum connects with the engine on. And just double check all of your work in general, make sure you replaced all the hoses in the correct locations. God knows there's a TON of vacuum lines on our engines half of which are completely unnecessary but all of them can cause issues like this if connected wrong or leaking. Lmk how you make out.

 

Thank you. The problem cleared up after about 8 minutes of running. Turns out, the throttle body cleaner I heavily used on the upper air intake manifold, needed time to run through the system. The local auto parts guy told me the same thing. (to run it 8 - 12 minutes to give the cleaner time to run out of the system) Right after I came out of the parts store to follow his advice, poof, idle surge automatically disappeared. I am glad it was not a vacuum leak.

 

Nice! I'm glad to hear you got it sorted out man.