My guess is that you created a vacuum leak. The EGR valve is not open at idle or rather it is not supposed to be - disconnect the vacuum line to it and verify that it makes no difference. If there is vacuum in the line at idle the EGR will go open and mess with idle. I would place vacuum to the valve and verify that it does mess with idle. The point being to determine whether the valve is closing (they have been known to stick).

There is nothing you should have done that requires any computer resets except maybe clearing old EGR codes. While HFM cars adapt slowly the closed loop O@ sensor control should handle mixture and will correct for vacuum leaks to a point. On a HFM car the adaptation to limits could take a week or more to set a light if a new air leak can't be adapted to.

Make sure the EGR pipe is sealed at the back of the head at the union. I had a tech aquire that leak once on cylinder head removal. The systems almost covered it up. The only symptoms was a varying idle speed.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician