It sounds like the BCDD. It might just need an adjustment. The BCDD is supposed to hold the revs on decel until the car gets under 10 mph and then slowly drop back to idle. Mine was doing the same thing as yours, but hanging at a bit higher rpm. There is a screw on the bottom of the BCDD to adjust it, but I didn't have any luck moving mine. I decided to disable it and the car now runs much better. If you decide to disable it, remove the rubber intake hose between the AFM and the throttle body. You will see two holes at the bottom of the throttle body. One hole goes to the BCDD and the other goes to the distributor if I remember correctly. If you plug the hole that goes to the BCDD, it will disable it and make your car run better (assuming you can't get the BCDD adjusted properly). In my case, I used a piece of QUALITY tape to cover the BCDD feed hole TEMPORARILY so I could determine for sure that the BCDD was the culprit. As a precaution, I cut the strip of tape long enough to extend upstream and wrap around the opening of the throttle body so that the rubber intake hose would help secure it in case it came unstuck. I didn't want to risk sucking it into the intake. Make sure the tape covers the BCDD hole only (the larger one) and does NOT obstruct the butterfly valve. After replacing the intake hose, take the car for a quick drive to see if the problem is gone. If so, the BCDD was the problem and you can either replace it or disable it by plugging the air hole with some RTV. On my car, the tape trick worked, but at the same time the idle was much lower and the car would stall when coming to a stop when the car was cold. This told me that the AAR was also not working. I replaced the AAR and the car now runs great cold and warm.