Well that would indicate it's going lean at low throttle settings. Have you tried the TPS recal routine?
From another thread
"Had a couple of hard starts, unexplained. Then yesterday and today had the idle go to 2600 rpm then slow down to about 1800, THEN start surging to 2600 rpm and back to 1800-2000 rpm. The fix was not the TPS (throttle position sensor) but to reset TPS and ISC (idle speed control or air bypass valve):
Key off, start-run switch on
Open throttle full and hold
Key on for 8 seconds
Close throttle
Key off
This initializes TPS and ISC and the problem went away. Normal idle 1650-1800 rpm and no surging. I don't know what the cause was other than guessing TPS "changed" a little with use."