27.. I used to have the same issue on my 99. Exact same issue.

I ended up taking the throttle body off and cleaning it. Don't use carb cleaner to clean it with the sensors hooked up. I took mine completely off and removed all the sensors and let it soak in a coffee can of gasoline for about 45 minutes and scrubbed lightly on the inner portion of the throttle body. You'll be very surprised how much crap you get out of it. They just get gummed up over time.

I did mine at 77K when I did the upper intake and lower gaskets. When you do clean it, make sure you reassemble it with a fresh throttle body gasket. The old ones aren't meant to be reusable.