So i bought a turbo miata a while back. Its a custom setup (no need for too many specifics for now), first the damn car has a jet ski tiny *** battery (no joke), basicaly good only for track. So it would die a lot, and then the coil (external 1.6 went, and it took me forever to figure out that that is what it was, and car was trying to run on 2 cylinders). So I put in a new coil, gave it a wash and started driving it after a couple months of it sitting. Again i noticed battery is useless, like even playing the stereo for an hour would cause the gauges to start dimming. So then I'm driving from girlfriends house, and I stop at a stoplight. Almost stall the car and barely catch it from like 200rpm. This is when it begins...

Car jerks violently as I accelerate, like its going on/off constantly and continuesly. Shifter shaking hard. So I make it home and Im worried I broke something (by almost stalling the car?). It starts to smooth out (but still slightly present) as Im driving home. Symptoms appear strongest in first 2 gears, and in the lower rpm (below 3000). Also symptoms dont seem to appear if I'm giving the car minimum throttle, only when I give it any more that that. I get online, talk to some buddies, he tells me his turbo miata did the same when his battery was dying. So I relax, because I've had problems with the battery and assure myself its the battery.
Next day I put in a stock used battery, I know its good because the other miata fired up flawlessly. Take the car for a spin around the block, seems fine again (maybe a small stumble, wasnt sure). So I'm happy. Start driving the lady home, symptoms back. Now let me tell u how frustrating it is when the engine is revving in hiccups. So make it to her place, turn off car, let it cool for 5 minutes, pull the spark wires from the coil, put them back in (in the dark)...car running flawlessly home. Then as I'm getting home symptoms start returning, not as severely as before. Checked spark plugs, they are dry. Did I spin an engine bearing or break something by almost stalling the car (not a mechanic)? Because the car has had low battery many times, and it did not do anything like this, and this specifically happened after I almost stalled it...and I have stalled/almost stalled this car quiet a few times.

Specs:

Custom intercooled turbo setup, heatwrapped turbo, makes good boost and running prob only 7-8psi right now...
E-Manage Ultimate, good stable map, ran flawlessly for a couple months
Rx-7 Injectors (470cc I believe?)
8.3 Compression (headgasket)
Some bad *** clutch made to handle 250lb/ft +
Chromoly flywheel
The car has a pretty trick alarm system, and I suppose it drains some...

Some info: idles fine...mostly (saw it dropping off a bit on the way home)
40psi fuel pressure at idle.
Great oil pressure.

Anyways, if you can help me figure this out or at least reassure me that it cant be that bad, because I'm afrraid I have a costly problem that I cannot afford right now. I will make love to each and every one of you. Promise

 

The battery shouldn't be draining like that. How often do you drive the car? If it is only every few weeks the alarm is killing the battery, other wise you probably have bigger problems, likely with the alternator.

are the plugs, wires, etc in good shape? those can cause pain in the *** problems like this.

Otherwise I would be suspicious of something going wrong with the piggyback wiring. If you have an intermittent connection on something there, it can cause big problems.

Almost stalling the car won't have caused any sort of mechanical damage. Your problem with this car is almost certainly electrical.

 

When you said you put in a new coil, was it a brand new OE piece?

 

this sounds like plug wires too me
get some news plugs and wires and give it a shot, make sure you clean the terminals on the coils
i assume you have a 1.8 car, no?
also, RX7 are either 550's or 460's or 440's not 470's

if problem persists, check all your gound wires, next to TB and under heater core hoses you have a ground for the head
good luck

 

remove the alarm system, get a good new battery, replace plugs and wires. if the problem is still there, then ask again.

 

check for vacuum leak it can cause a problem like this

 

Vacuum leak is reasonable, but I would definately start with coils. Especially since you said wiggling the plug wires made a difference. I've seen that happen before. Plug wires go all the time on miatas. Coilpacks do too, to a lesser extent. It's the best place to look.

 

Figured it out gents. I didnt understand why the problem was intermittent, so I thought about it and its happening only @ night/very early morning. And that when we have -3 degree weather.

So here is the story:

There was a fire in the engine compartment at a track, so wideband and oxygen temp dont work. So the wideband was reverted to narrowband and the car was running on a map. However, I guess because of the much denser air, and because the EMB is no longer modifying the map based on AFR, the car is running lean or going into limp mode. So I dont know if its just the sensors or the whole wideband module (LC-1) is gone, but I wont be driving the car until the weather improves and I can fix the wideban 02. (Quick noob question: the wideband sensor is the one that plugs into the downpipe and you can see from the engine bay? Where the 02 is right?)

Thanks for all the help.

 

wideband not working maybe you need to replace the bosh sensor or recallibrate it. how does your status LED look if you have one. does it stay on ? does it keep blinking? if you have a good tune you can try that out by uploading it on the EM and turning off the autotune feature so that you don't mess up the map.

 

There is your issue... fix the damn AIT. Intake temp is very critical to the fuel calculations used when running off of a MAP sensor. With no AIT you are skating on thin ice. Be thankful you haven't already blown the motor.

 

By this you mean get the wideband to work correct?

 

The autotune feuture HAS been off, because the wideband is not working.

 

Where in my post did you read wideband? I meant what I said. The AIT is very critical to fueling calculation, without it there is no chance in hell of having a consistent or safe tune.

 

I dont know wth AIT is nor how to fix it. Air is colder, so its more dense, autotune is off because its on narrowband and it not accurate. I assume solution is to get a new sensor and switch the autotune back on once wideband is read accurately. Then the emb will be able to compensate for the denser air based on AFR readings. The previous owner had a good tune, its just not being dynamically changed based on AFR because wideband is non functionall.

Explain what u mean plz by AIT, i have no idea of that acronym... air intake temperature? And the only way i see for that to be determined is with a good afr reading, which needs a new sensor for the wideband 02 to work...

 

I think hes talking about the AIT SENSOR if its reading a different temp than whats really entering the engine then its gonna throw off the whole tune

 

My AIT sensor should be fine...

 

hi every one i am a new guy on this site i have a 00 miata running 500hp im having a problem i keep breaking my diffs and gearbox and im wondering if the gearbox and diff of a 2nd gen rx7 would fit and work in my car.thanks

 

oxygen temp = intake air temperature sensor.

You said it yourself.... it's broken. FIX THAT ****.

 

off topic. start a new thread or use the search function.

 

Im so sorry lol. I didnt even realise, I meant exhaust temperature sensor is down (not oxygen). Lol, thats all the confusion, yea there is no way in hell I'd run my car like that, not that stupid. That is why I see the 02 as the only possible problem? Autotune has been off, so Its not adjusting the map to the denser air...