8 is in trouble. Shutting off when I stop
 

Okay everyone. My 8 is giving me problems. I have done a tune up by changing all plugs, wires, air filter, cleaning MAF sensor, cleaning throttle body, changing fuel pump, checked battery level, checked alternator, and starter check. I did a compression test and it was very consistent across the board. (I will post a pick of the compression slip that the tech gave me.) I have tried pretty much everything but to no avail. The car runs fine up start up and idle but when I stop at a light or sign then I run into to problems; the RPM's drop below 1000rpm's and then it shuts off. I have read the forums with the same issue but no one really offers a solution that they found. Please offer some help. I really don't know what to do anymore.

did you disconnect the battery? if so your car is re learning fuel maps iirc and should be fine after a few drive cycles. has this been going on long?

Here are the pics
 

See attached

Yep. I disconnected them when I changed my front suspension (1 week ago) and when I did my abs sensors and fuel pump(yesterday). Could it really be that simple! How long does this take to relearn?

mine doesnt always stall at a light but has in the past. a few drive cycles would clear it up pretty quickly. i dont know what your pics are. comp test?

Yes. Those are the pics of the compression test. The slip is kinda long, so I coulnt send as 1 pic. I only included in case some asks that questions.

Should be obvious but you have bad compression, almost hitting 6.0. If you have a warranty get it replaced while you can.

My assumption of the pictures showing the compression test. The picture is of each rotor face compression, so each peak on the picture is a different face.

ive never seen a comp test like that before. where are you from? was it done at a mazda dealer?

That's an analog compression test, however it is mostly sufficient since you can see the tips of the wave, which is the peak compression point, and every 3rd peak is the same rotor face. If your cranking RPM is ~220rpm or more, your engine is failing. The symptoms agree with that as well, as your idle speed isn't generating enough compression to remain alive. I would guess that when it shuts off, it's hard to get it fired again for a while, until the engine cools off some.

At 250 cranking RPM, the tips of that compression signal wave needs to be crossing above the 7 kg/cm2 line to not be failing.

Are you saying that my engine is failing even though the compression test says otherwise. And when it shuts off then it cranks right back up but it will shut off again unless I keep my foot on the gas or sometimes it just dips under a 1000 then sits fine until I drive again but it ultimately shuts off again when I stop

No no, we're saying your engine is failing BECAUSE of the compression test. Mazda states that for an engine to be classified as not failing, both rotors need to have a compression of 7.0 kg/cm2 or higher at a cranking speed of 250 rpm.

As you can see in your photos and paper you received, the peaks on both rotors is barely above 6.0, unless the cranking speed is below 220 rpm, your engine failed a compression test, doesn't matter that it was consistant.

What octane are you using, and have you cleaned the ESS, checked for pending codes? Could be the simple fact of what RIWWP said, not good enough compression to keep it's alive while idling.

blckninja is correct. Assuming that you have a cranking speed of 220rpm or more, your compression test slip shows that your engine is failing. If you don't know your exact cranking RPM, you need to get it, because if you are under 220rpm, then your engine is not failing (just 'weak') and the issue is elsewhere. However, you addressed everywhere else it might be and have a compression test showing failing scores so......

The failing line at 250rpm is 6.9 kg/cm2

On the dying at idle.

The re-learn is tough. Best way is start over, disconnect battery. 20 brake stomp for good measure, then just start it and let it sit until the idle comes all the way down. At the very end, you may want to turn on the AC to bump the idle a tad. After that, it has learned to idle, and will learn the rest while you drive.

I would think that after a week it would have learned though, what would be stopping it from relearning how to idle?

Low compression means that there is a lot of air and fuel being unconsumed, blowing by into neighboring faces and getting dumped into the exhaust. This is a random mixture of air and fuel (relatively speaking compared to normal), and the front O2 will be swinging around on AFRs, and the ECU will have a lot more trouble figuring out what fuel trims need to be applied, and what it does figure out will probably be wrong.

Ah that makes sense. But then trying to get it to relearn would be a waste of time until the engine is replaced correct?

In general, yes.

The trims will keep building anyway, regardless of if you "try" or not, but don't bother trying to wait on them.

Goal is to create as stable an environment as possible for the ECU relearn. But yeah, if it is worn, it is still worn. But, if the ECU is trying to learn, while you are driving, and load and RPM are fluctuating all over the place, it will take a lot longer.

That engine does look like it's failing. It's barely above the minimum acceptable 75 PSI and well below the nominal 110-150.

That said, the battery disconnect and learning mode comments are also correct and generally, you perform an ECU reset after disconnecting or connecting a new battery.

I had the same stalling issue with mine after adding coils and a cat until re-setting the ECU, pretty much every battery swap.

Not to make anyone repeat anything but how exactly do I perform a reset on my ECU?

Dont bother. I found it..