1999 Miata 'Slow' Start Issue

This is going to be a somewhat long post, but i want to detail everything that i have tried thus far.

There was a hole in the rear plastic screen of the vinyl top, and had a really bad rain storm before i could get home and pull the mazda into the garage. Inside the cabin, the ‘shelf’ where the top would sit if it were down was pretty wet, so i taped up the gap and decided to wait a few days until everything was dried out before trying to drive it again.

The vehicle is driven usually once or twice every other week (it’s a second car that I use to play around in on the weekends).

After driving the car for a little while, came home and parked. Then for whatever reason, I turned on the headlights, and the idle dropped off and car felt really rough. OK, not sure what it is, I’ll turn the car off and fire it back up to see what happens.

When trying to start, basically anyone in the north can picture attempting to start a car in -15F weather without having a block heater. (its 80F at the moment)
VERY slow turnover for a few seconds until it gains some steam and then the car fires up. Also fires up just fine when jumping the vehicle.

Here is what i have done so far:
1.) Pulled battery and put on trickle charger over night (solid 12 volts after charge)
2.) Re-installed battery, fired up first time (Can’t remember if it was slow to start or not), let idle for a few minutes, then turned off.
3.) Tried to re-start and very slow turn-over until eventually car started (turned over about 6 times i would guess)
4.) Ran all accessories (AC, radio, defrost, four-ways, foot on break, headlights on high) Checked voltage across battery terminals and got about 14V and change. Also vehicle idle did not drop off and vehicle did not run rough.
5.) Turn car off, measure voltage of battery at about 11.96 or so.
6.) Checked voltage after about 12 hours, voltage reads 11.95, so I’m thinking that nothing is discharging the battery while key is not in.

Any suggestions to diagnose?

Thanks in advance.

My guess is that you need a new battery. If the car starts normally with a jump start, this is a clue that the battery isn’t supplying the power that it should. Normal battery voltage for a fully charged battery is about 12.6. I would bet that a load test of your battery would indicate that it isn’t producing the amperage that it should.

Looks like i also forgot to point out the battery is less than 1 year old. Will try and dig up the warranty paperwork as well and get the battery tested. One final bit of information, when key is turned to accessory, i am hearing an electrical buzzing sound coming from right front of engine compartment, but haven’t isolated it enough yet. I will also be checking all the grounds I can find in that area.

The age of the battery is irrelevant. I had a brand new battery that didn’t make it through a week-end. When I bought the battery, the engine cranked slowly, so I put the battery on a trickle charger overnight. I checked the battery voltage after I charged it and it was 12.6 volts, so I assumed all was well. However, my son had the car out that night and reported that it cranked awfully slowly. I measured the battery voltage and it was about 10.8. I put it back on the charger for overnight and the next morning it read 12.6. I disconnected the battery and checked the voltage after 2 hours. It was back to 10.8. When I returned the battery, the clerk didn’t want to exchange it. I insisted he load test the battery, but he claimed he didn’t know how to do that and I needed to check the alternator in the car. I grabbed the leads to the load tester and said, “I’ll show you how to use it”. The load tester indicated that the battery was defective. The clerk then told me that they didn’t have any batteries in stock like the one I bought and I would have to buy a more expensive battery. I then asked for my money back. I was told that the store couldn’t do that since I had traded in the old battery and my old battery had already been picked up for recycling. I finally demanded to see the manager. After some argument , he gave me an old battery and I went to another store and bought a new battery. What was disappointing was that the store, a chain farm store that is now defunct, had been the place where I had done a lot of business–tires batteries, lawn mowers, a lawn tractor, and so on. I never did business there again.