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To begin with, this is my first post I've happily owned my (D17A2) 2005 civic EX special edition for 2 and a half years, and i've never had any issues

Until recently when I had the dreaded blown headgasket, with coolant gushing out of my overflow reservoir. So I got the 40 something piece felpro gasket set. (ive owned many types of cars but i only use one type of head gasket) I also installed a dayco timing SET(w/p tensioner & belt) and all new motor mounts while i was at it.

the issue only arose during the test drive. At idle while the car was warm, I would feel a heavy vibration at idle, ALMOST like a misfire, but not. Even weirder was that the idle was steady at 750 rpm. The engine wouldn't try to stall or anything, even pulling up to a stop sign and stopping quickly.

while researching common idle issues with this year model civic, particularly this link https://www.civicforums.com/forums/3...e-posting.html

I checked everything that was listed (twice) with very slight improvement (probably the75k on the plugs) but still a heavy vibration in the shifter and steering wheel. I even swapped all my new motor and trans mounts back to the factory ones to no avail. I was just about ready to give up.(re-installing the plastic intake plenum) then I thought what if the EGRV was clogged(knowing it opens after the motors warms up). When i finally got it off it LOOKED clean but looks can be deceiving. I took the EGR and flipped it over and filled the port(the valve its self, not the passages into the head) with throttle body cleaner and let it set for 5 minutes then poured out the excess(which was only slightly brown) and blew out the EGRV with compressed air (reg @ 120 psi)

After reassembly it was night and day. Steady idle with NOOO vibration in the shifter and only slight rumble in the steering wheel(just enough to know its running) even warm i couldn’t be happier!

I've seen a few other threads that were never solved with my identical symptoms. I think it happens quite often, so i wanted to toss in my 2 cents and give people another vector to look for an "idle issue". Personally i think the idle issue post in the Mechanical Problems/Vehicle Issues and Fix-it Forum should be edited to show this possible fix

 
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Thanks for posting that..hopefully, it will help those with similar issue.