I know this is an old thread, but i am just now seeing it. Did you ever figure out what was causing this?
I have a 2006 XLR-V that I got about 3 years ago. About a year ago I put K&N filters in it. (I love them & put them in every vehicle I own, but for some reason didn't do it immediately with the XLR like i usually do)
After replacing the filters i noticed that the car did not decelerate as "aggressively" when I let off of the gas while driving it harder, & that it returned to idle slower when driving it more mellow. I assumed that because the engine is getting more air flow, the ECM is sending more fuel which is causing this condition. I've been kind of torn on whether to change back to the stock filters or not. I can tell there is an increase in power with the K&N filters, but the car definitely feels more aggressive with the stock filters & then of course there is the issue of the slower return to idle...
Now I just want to make sure that there might not be some other issue that coincidentally showed up at the same time as my filter swap.