Certainly sounds like an IACV. Clean it out and see how it goes -- Id also be looking for vacuum leaks (cracked hoses or seals) on the intake side. Throw a scanner on it and observe fuel trims at idle.

I wouldnt worry about switching from E10 to EF, I doubt you will notice any difference but also won't hurt anything.

__________________
TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth