I have a 2008 HHR 2.4 manual trans. Now I have a tune file with factory settings and two tune files from two different tuning companies. When changing between these three tune files (to compare performance, behaviour etc.), I always immediately get wildly fluctuating idle revs.

Idle revs when not moving go up to 2000 or 2500 or so from the default 800. Same for idle revs when moving (clutch disengaged). It usually seems to take about 80 miles of driving over a couple of days (at least that's my normal driving pattern) for the idle revs to settle back to normal.

Is this expected behaviour? Can it be avoided somehow?