I tried to start up my Miata for the first time in three weeks. When I went to start it, the battery was dead. No sounds, no lights, nothing. So I go and jump start it, which it does on the first try.

Then the lights start to flicker...

I rev it up and the flickering goes away, but as the RPM's drop, I hear a gurgling sound from the intake, as if it were underwater and the lights flicker again.

If the revs are up, the lights are bright and everything is normal, but when I let up on the throttle, it gurgles and all the electricals flicker again.

Thoughts?

 

Does it idle like normal while lights are flickering? First thing I would check is the voltage and amperage coming from the alternator. Does the battery hold a charge after running for a while and start back up? Next I would check the condition of the battery. Are the battery connections good? Possibly a ground too.

 

Keep in mind that your alternator does not operate very well at idle. The rpm's are too slow for it to output not only a good amperage level but also hard for it to maintain a good voltage. If your battery was completly dead then either let the alternator get a good charge on the battery or better still use a trickle charger to get battery back to charge. The gel batteries used in the Miata are somtimes a little difficult to recover from a full discharge. A slow charge for at least 12-24 hours will usually restore. Get the battery back up to a normal charge level before worrying about any flickering lights or gurgle noises. I think you will find both of these problems will go away once the battery is back to normal.