One other question - have you noticed a "shudder" when turning off the ignition? If so, it might be a clue that you've got CBU on your throttle valve that is preventing it's normal operation. I'm told (see
post #3 on this link) that another name for the throttle valve on diesels is an "anti-shudder valve." I had noticed just such a "shudder" before embarking on my various CBU cleanings about 6 months ago. The "shudder" went away afterwards and (knock on wood) has not yet returned.