plugs are coked in carbon

tail pipes are black

Go to the auto parts store and buy an under hood (or hand held) fuel pressure gauge and check your pressure. I believe your super rich condition could also be leading to a "missing" symptom.

Update:

so I took it to a 'mazda' garage.

he believes the missing is due to a faulty coil pack and the rich conditions are due to a faulty AFM.

i have never changed these since owning the car.

I have sourced a good second AFM and coil pack.

I have also got myself a new water thermosensor, new PCV valve and plugs.

will fit these and report back.

I burned a 1/4 tank in less than 10 miles once when my AFM died...but thats when it actually freaked out, I'm surprised it actually ran lol

just fitted the afm.

O2 sensor has died unfortunately. I can tell as it is no longer oscilating on my a/f guage. I ordered another 4 wire today.

Had a short drive and it may be too earley to say......but the car is allot more responsive, does not bog down and feels faster.

Will monitor over a week and report back.

Tomoz the water thermosensor will be replaced and so will the coil pack.

Fingers crossed.:cool:

if you've added the 4-wire O2 sensor, do you have it wired so the heating element will turn off after it warms up? if you have it wired to a constant 12+v source, it could be killing it prematurily.

I opened mine up to tighten the spring. A few weeks later my wife and mother in law took my car on a trip and broke down 2 hours from home. The spring had broken. I drove up there to get them and drive the car back (women are so damn stupid) and it used an entire tank of gas in about 100 miles.

The 4 wire o2 sensor has been wired as per the instructions on hakuna miata:

http://www.miata.net/hakuna/0004/aindex.htm

Also I changed the water thermosensor, coilpack and pcv valve yeasterday.

Did not notice anything apart from the fact its not hesitating now.

When i get the 4 wire sensor I will fit and monitor for a few weeks.

I am hoping my over rich condition will be cured now!::crx:

How did you wire yours to turn off? Looking for some ideas...

FWIW, I have never heard of killing your O2 sensor faster this way. I have my doubts that it works like that (12V heat kills it but 1500 degree exhaust does not) but I am open minded. What do you know about this?

I talked to someone about this today. Their comment to me is that the factory units (on 4-wired cars) are on all the time. So, no, I don't think there is a problem running it all the time. That is, IMHO, not what will kill an O2 sensor.

i have changed the 4 wire o2 sensor.

before it was throwing code 17 - Oxygen sensor (output not changing)

but it is still hesitating and the MPG does not seem to have improved although my AF guage is now oscilating a gain.

could I hae wirw the heater wires incorrectly?

I have not checked for codes since the install tho.