We have seen this issue many times and in most cases it is the cause of a slot in radiator shroud for a CAI that was cut too high.
This hole must be cut very low in shroud else if high there will be 2 negative effects.

1. Incoming air close to the MAF will be seeing turbulance which causes ill efects on decel and low engine loads.

2. The higher the cut in shroud is the closer it is to the A/C condenser and its heated air bouncing into the CAI and into the MAF

In this case owner has a C5 Z06 where on lifting off gas pedal (decel) or at low engine speeds the engine would surge and also sluggish.

We had owner do a slow speed testrun with a Ease OBD-II scanner recording and then he emailed that to us to analyze

When we saw the following we then knew what the problem and fix would be

The fuel trims on average was 5% lean but this also was done in 90 degree weather.

You notice though when looking at each fuel trim cell which were much leaner.
What you see is cell 21 (decel) and the cells to the right of it are quite lean yet the MAP and vaccum show butterfly of throttlebody is closed so little air would be reaching engine to be that lean and thus air turbulance was the problem

Fix was simply in having the owner reduce the height of the cut in shroud so that the cut was low and then only 2 inches tall.
This prevented swirling air going right to the MAF and also the colder air to enter the air cleaner