Just thought I'd lend my 2 cents. Thanks to ALL you guys for helping me resolve and repair my rough/rolling/dipping idle issue!! Here was my problem:
1) Rough standstill idle -- needle hovered up/down 50 RPM from 700
2) Occasionally wanted to stall after a warm start -- RPM dipped to 500
3) Poor fuel economy -- about low 20's
4) No DTCs -- wheww!
5) Engine vibrates/shakes
I performed the following operations:
1) Changed air-filter (ash inside from recent fires)
2) Changed spark plugs w/NGK V-power; old ones were Bosch Pt and were slightly burned at the tips and overheated at the plug boot part (orange ring).
3) Removed, cleaned, lubed and re-installed the EGR valve assembly:
a. this was a serious PAIN to perform! From under the jacked car (on stands), I used three drivers: 3/8" 90 deg swivle socket wrench, 1/4" flex "T" 90 deg socket wrench and 12mm offset boxed hand wrench. It wasn't on too tight. Found it was definitely full of carbon but operating within specs. Used Liquidwrench for the 4 screws. I checked resistance and plunger operation -- all okay. I used SeaFoam Deep Creep and blasted that puppy. Everything was cleaned. Some carbon remained on plunger but freely operated. I pre-installed the bolts & gasket on the assembly and placed blue painters tape over the bolts to hold 'em while squeezing everything back on the manifold.
4) Removed and cleaned IAC solenoid assembly plunger and mounting area on IAC core. Used T-25 tamper-proof screw bit from Craftsman. Piece of cake to do -- used Liquidwrench on the two screws to make life easier. Lots o' carbon on solenoid plunger and mounting area. Plunger sticking to IAC mount. Used SeaFoam Deep Creep to clean.
5) SeaFoam motor treatment through PCV system into intake to remove carbon build-up; used 6 oz. The trick is to have a second person maintain a fast idle while the solvent is slowly sucked through and cut engine.
6) inspected many other parts and found no faults (e.g., PCV, purge control, PS pump, plug wires, vac leaks... I was up until 1:30AM one night! Reset PCM.
Startup and Roadtest: Very close to being a new engine! The motor vibrates some -- good for 67K miles -- but is noticeably smoother. RPM is very stable and so far no unexpected dips. Passed all load tests.
UPDATE: I added a SeaFoam motor treatment to the list and engine has become very smooth. Successful repair cost under $100 including two new tools in my garage arsenal for future sagas!