Fast deceleration problem
 

1986 RX7 GXL (automatic, I know, I know,bad)
I'm the original owner, still has all original parts, no modifications.
Issue: When I must decelerate quickly (like when I'm coming to a stop light that's already a deep shade of yellow and the rpm's drop quickly (while braking), the needle drops a little lower than normal idle for a split-second. It almost stalls before recovering to normal idle.
Under normal gradual decelerating, no problem.

Net: it seems to be slow to switch to idle from normal running.
Could the idle be set too low? Could increasing the idle a little give it a little more time to respond to the rapid drop in fuel feed?
The problem seems to be aggravated if I have extra load, like the A/C on.
Any thoughts would be appreciated.

It could be electrical, since the brake lights come on when you press the pedal. The S4 alternator is weak (70A), and in the past I've been able to affect idle with electrical load. Grounds can also play a role.

It could also be a vacuum leak. In particular, the hoses used by the brake booster. There is one coming off the intake manifold and another at the brake booster itself.

Does this problem you speak of occur only when the engine has recently been started and is in the process of warming up or it does this regardless of how long you've been driving? If it does it only when the car is warming up then I'd like to ask you if your car idles properly upon a cold start or does it have a bit of a bouncy idle until it warms up.

satch,
It's only after the car is completely warmed up and the idle has dropped to is lowest setting. No bouncy idle when cold or while warming up.
Sorry about the slow response. I have not been on the forum for a couple of days.

There is an item bolted to the back of the throttle body closer to the passenger side called the "Dashpot" and it is repsonsible for preventing the car from stalling during a quick stop. Check the FSM for how to check/adjust the item. If you find that's not your problem then you could find a place where you can drive the car trying to recreate your problem but first disconnect the plug with the Green/White and White /Green wires which are connected to the brake light switch. W/o the plug connected you won't have brake lights so be careful of this but in disconnecting the plug from the switch located above the brake pedal pad you will prevent the car's voltage from dropping any when you depress the brake. Doing this test will help to identify whether a voltage drop is contributing to your problem. Your problem might also be associated with the BAC as it helps to prevent a drop in idle below 750 RPM when things such as the A/C create a drag on the engine. Your idle should be at least 750 RPM at all times but not really higher than 800 RPM. My car does something similar but it never stalls and the RPM only drops for a brief moment.

Thanks satch.
I printed your information about the Dashpot'.
The car is scheduled for an inspection sticker next Tues. The shop (they really have good mechanics there)
I will pass on your info. I have already mentioned the idle thing to them and they are planning to check and make any necessary adjustments.
I'll let you know how I make out. I know my wallet will not do well. Small problems always seem to become bigger when I try to address them.
Thanks again.