Had a little problem today, already fixed it and thought I'd just post the symptoms & solution.

Symptoms:

- Idle fluctuates from 200rpm to 600rpm, engine will stall unless accelerator is depressed to raise rpms.

- Hesitation upon acceleration.

- Bad smell out of exhaust while idling.

- Symptoms go away on highway, while RPMs are higher.

- Check Engine Light, DTC P0404 set.


Problem:

- EGR Valve stuck open.


Solution:

- Remove & clean EGR valve.

- Check EGR passages in the water passage (holes under EGR valve) for loose carbon chunks.


In my case the EGR valve itself was fine, since I had it off I went ahead and cleaned it.

However when I looked into the EGR passage in the water pipe there were two large pieces of carbon sitting there. They were being sucked into one side of the EGR valve and holding the valve itself open while not passing all of the way through the EGR.

I used some long needle-nose pliers to grab them out of the EGR passage and followed by sticking a vacuum cleaner nozzle on the ends of the EGR passage to hopefully remove any further loose deposits that I couldn't see.

Re-installed EGR valve, ran the car and idle is fine again.