Upon closer inspection, yes, the bolt heads do require a 5-sided instead of the 6-point torx tool. I will find the correct tool and proceed. Thank you.
MAF O2 sensor contacts are also worth cleaning (remove 2 Phillips screws to get at it). I used CRC contact cleaner to clean mine. Another common item worth taking a look at is the PCV valve. The PCV valve in my 2000 was so gummed up I simply replaced it ($10 for an OEM replacement). I had a similar problem as yours, except to the point that the car would stall when cold. I thought I had it fixed after replacing the PCV valve, but its still there. My next step is the same as yours - to clean the IAC valve.
The bolts on mine are so badly stripped I can't tell what they originally were. I picked up some heavy duty hand tools yesterday that included various types of pliers, so I might finally be able to get them off, and when I do I'll replace them with simple Phillips of the same size.
-Spyder