2015 Mazda5 Stalls at idle, just shuts down...Help!

[zentoed]

Hey all, first post, looking for some ideas.
I've got a 2015 Touring, 125k, that has just started stalling at idle. The idle is not (very) rough or low. No trouble codes, no check engine light. It will start immediately after and I just drove it home, 20 miles with no other driveability or performance issues. It will idle and then instantaneously shut down, no stumble, no change in idle speed, no cough or sputter, just die like someone has turned off the key.

I replaced the (original) spark plugs, and it hasn't helped. I cleaned the throttle body as well. I also probed two of the ignition coils while it idled and then stalled, it did not lose voltage to the coil when it stalled.

Any help would be greatly appreciated.

 

[edmaz]

Hey all, first post, looking for some ideas.
I've got a 2015 Touring, 125k, that has just started stalling at idle. The idle is not (very) rough or low. No trouble codes, no check engine light. It will start immediately after and I just drove it home, 20 miles with no other driveability or performance issues. It will idle and then instantaneously shut down, no stumble, no change in idle speed, no cough or sputter, just die like someone has turned off the key.

I replaced the (original) spark plugs, and it hasn't helped. I cleaned the throttle body as well. I also probed two of the ignition coils while it idled and then stalled, it did not lose voltage to the coil when it stalled.

Any help would be greatly appreciated.

Live OBD data might help diagnose the issue, particularly MAF and MAP readings. But if you don't have one of those tools available, then (with a helper revving the engine to keep it running) try spraying a small bit of sensor safe starter fluid into the intake, to find out if it will stay running with supplementary fuel when it drops down to idle RPM.

 

[zentoed]

I drove it today another 20 miles.
I parked it and let it run for over an hour, drove it 5 miles, parked it and let it run again for over an hour... it hasn't stalled yet.
I will say that after I replaced the plugs, it did not stall after 3-5 minutes like it did before. It ran for 10-15 and I thought I had it fixed. I shut it down , no stall, and I changed the oil and cleaned the throttle body.
Then I let it run for 20-30 minutes an it stalled.
But it hasn't stalled since.

I will see if my scanner will do live map maf readings, but will it tell me anything if it is no longer stalling?

Thanks for the input

 

[edmaz]

....
I will see if my scanner will do live map maf readings, but will it tell me anything if it is no longer stalling? ....

It's unlikely that the root cause of the stalling would show up in the live data if the problem isn't happening. And if the stalling doesn't happen all (or at least most) of the time, then it becomes much more difficult to figure out what's going on.

The non-sputtering stall that you described IMO sounds like an electrical issue, even though you saw coil voltage while it was happening. Did you check the static and running voltage of the battery? If those readings are fine, then here's one more test to try.

For this one you would need either a helper behind the wheel, or long leads attached to your multimeter, so you can see it while you're running the electricals. The test is conducted by turning on everything electrical, one-at-a-time, and watching the meter as you do so. Don't touch the gas pedal at any time during the test. You should see a brief voltage drop for some of the electricals, but a very quick bounce back up to the original running voltage (or at least very close). Leave each thing on as you go through them, until everything is running. If the charging system is ok, then the running voltage should still look good with everything running.

 

[zentoed]

So it seems now that the problem is worse when the AC is on. Wife just reported multiple stall and restarts with AC on, in drive, waiting in drivethru.
Turned AC off, and car did not stall.

So I have more info now, to help when I can look at it again

 

[zentoed]

Damn, I just wrote a three page update and lost it due to some glitch.
Long story short, idle relearn may have done the trick...
I'll try to update again later.
Wish me luck!

 

[MarioT]

Suggestion I got for you if the problem gets back:
Clean the Throttle butterfly with a toothbrush and carb cleaner.

I had weird idle issues too on my 2015 around 70kmiles. Near stalls while stopping on red lights. Unstable idle when the AC compressor cycles..

Cleaning, then relearning idle made it work like new.
Also, the weird flooding issue (short 2 mins run, then restart later) I had once in a while is gone at same time.

 

[zentoed]

So, I drove it at least 60 miles yesterday, after the idle relearn. It stalled once in the first mile and has been fine ever since.
Before the relearn, it stalled 4 times in the driveway, with various AC on-off, park-drive setups. Each time it stalled in under 3 minutes.
After relearn it ran 10 minutes with no accessories or added loads and then 10 minutes with AC on.
MarioT I did clean the throttle body with "throttle body" cleaner and a soft paintbrush 3 days ago, but I did not do the idle relearn at that time. It ran better initially but then started stalling again.
So, after the relearn and 60 miles yesterday in stop and go traffic, and pulling into multiple parking lots, repeatedly stopping and idling in drive, it has been problem free.
Another long drive later today.
We'll see if it holds up.