I need help with a slow rev issue
 

1979 RX-7 totally stock 254K on chassis, about 30K on the motor

My car really does run great overall, so this is more of a minor irritation more than anything.

When the car is in neutral and I rev it up to about 6K it revs quickly to 6K and sounds just fine. When I lift off the throttle the car is slow to return to idle. What are the possible causes for this? Could it be something emissions related?
Thanks

Is this a new issue? There's a dashpot on the throttle that controls the speed of the throttle return to close.

i bet its ur fuel filter check that, does it backfire?

I agree with purple82, its supposed to do that. The dashpot should kick in around 3000 and slowly ease it back to idle. If it didn't the throttle would slam shut and you'd dump a lot of extra fuel down the intake.

It is consistently slow returning to idle even from redline.

How slow is slow? Even without the dash pot, my '79 still revs down fairly slowly. They have a really beefy flywheel, so all that inertia makes for a slower revving motor than the later model 1st gen 12A's. At least, that's what I figure.

What are you doing revving to redline in the driveway anyhow? ;)

Is this something that just started happening or is it just dropping back down to idle slower than you think it should?

The dashpot is there to keep your fuel mixture from becoming too rich during off-throttle deceleration. Without it, the car will backfire when you come off the throttle abruptly. I think it can be adjusted, although I've never tried.