Fixing the dreaded Idle Droop!

Acknowledgements: I got this tip from  the SSCOR mail list.

What is the Sebring idle droop on a 1.8 miata? This happens after your car has warmed up. When you come to a stop and let the engine idle, after about 20 seconds the idle drops 200-300 rpm and the car starts to shake, unless you had set the idle higher to compensate. If you have a vacuum guage, you can see the vacuum decrease  by 4 inches. Blip the throttle and the idle will go settle back at normal for a few seconds.  Then it drops again. If you're used to the steady smooth idle of a stock miata, this sucks!

This fix worked on my car. Locate the small rubber hose that is on the body of the Eaton supercharger. It connects to the air filter.  Put a clamp on this hose.
The clamp doesn't need to be very fancy. I just took two L-brackets and held them togther with a nut and bolt. For an elegant fix, use an aquarium air valve (brass - plastic will melt).

After clamping the hose, my idle went up 200 rpm. I adjusted it back to 800-900 rpm and it's steady now. No more idle droop.

I believe this fix works because this line lets the engine breathe air that's not metered thru the mass air flow sensor, so it's like a vacuum leak, Restricting it makes it a more controlled vacuum leak and the car's idle control system works better.

December 31, 1999