I've been doing 30K maintenance this weekend, replaced the plugs, grounded the car, cleaned the MAF and filter, and I've noticed that the car, even with the new "S" flash seems oftly rough during deceleration in neutral, and its not much better in gear.

I have had a couple of instances where the idle in neutral at a stop would jump around, I can't seem to replicate it for a dealer but I think my neutral switch may have an issue. Could this also effect the car at deceleration and the idle quality?

the rpms drop down quite a bit, and then bounce back up to near 1000, with the grounding, you would think that it would be better.

All these issues seem to happen with either the A/C on or off, but the A/C amplifies the effects. I know the "S" flash was a little rougher in decel, but this is worse.

Thoughts?

BTW, the FD spark plugs seem to work quite well at 1/4 of the price.

 

During closed throttle deceleration the ECU cuts fuel, then near 1500RPM you get fuel on first one rotor, the both as you get down to 1K.
This may be what you're feeling.

Maybe check the TPS. It may be signaling closed when you're not quite closed.

Yes the platinum plugs will work well, but they will not last nearly as long.