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ECU Relearn (warm start stalls)

Old 01-18-2011, 01:13 PM
  #1  
Clon3
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Default ECU Relearn (warm start stalls)

Recently I disconnected by neg battery terminal to store the car for 3 weeks. I just got back from vacation and noticed that the car will stall on warm starts. On cold starts in the morning the car idles fine, but if I start the car after it's warm, it will fire up and stall almost right away. Sometimes it works, but most time it stalls. If I give it an initial tiny bit of gas, it will idle fine on warm starts. I have read numerous posts about resetting the ECU through technosquare and tried it myself with no luck.

My question is will the ECU eventually relearn itself such as the proper idle rpm? If so, how long does this actually take? This never happened prior to disconnecting the battery.

PS: Car is a 2003 with about 70k miles. No engine mods at all.

Any help appreciated! Thanks!
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Old 01-18-2011, 02:17 PM
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Try the procedures listed here...

https://my350z.com/forum/engine-and-...procedure.html
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Old 01-18-2011, 02:44 PM
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Leave it alone.

I also disconnected the battery, and the Z "forgot" the idle. Did nothing and several days later it was fine.
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Old 01-18-2011, 03:43 PM
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Originally Posted by davidv View Post
Leave it alone.

I also disconnected the battery, and the Z "forgot" the idle. Did nothing and several days later it was fine.
Thanks Dave, did you mean you tried resetting the ecu and it did nothing? And several days later the ecu just recalibrated itself?

Thanks!
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Old 01-18-2011, 05:39 PM
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Originally Posted by Clon3 View Post
Thanks Dave, did you mean you tried resetting the ecu and it did nothing? And several days later the ecu just recalibrated itself?

Thanks!
Yes. I took no action. Just left it alone.
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Old 01-18-2011, 08:28 PM
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Originally Posted by davidv View Post
Yes. I took no action. Just left it alone.
Alright, it's been 3 days now and problem still occurs. Weird thing is sometimes it chokes and then magically revives itself and then idles normally... other times it just completely stalls out...

I'll keep monitoring it everyday.
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Old 01-18-2011, 08:44 PM
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I had the same issue. David is correct though to say just leave it alone. Mine took about 4 months to correct itself entirely. I thought my car would never be the same again it just takes time.
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Old 01-18-2011, 09:19 PM
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Originally Posted by marques1 View Post
I had the same issue. David is correct though to say just leave it alone. Mine took about 4 months to correct itself entirely. I thought my car would never be the same again it just takes time.
4months,... that doesnt sound right.\

I'll search around, but now I'm curious if this can affect reflased ECU's??
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Old 01-18-2011, 09:27 PM
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yes, mine took time to relearn. My batter died and i had to replace it. Once I changed my battery it started doing it the day after. I got my car checked nothing wrong no leaks no nothing. I kept driving it and finally it never happened again.
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Old 01-18-2011, 10:27 PM
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I'm hoping the ECU should eventually learn by itself.. it's kinda misleading if we had to reset the ECU and manually relearn all those throttle/pedal/idle settings described by others.. A battery swap should be fairly common, and I wouldn't expect Nissan to design something so complicated for the typical consumer to Know and HAVE to perform such a task....

Just doesn't make sense to me that a simple battery change would "require" a full ECU reflash just for the car to know how to idle properly...
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Old 01-18-2011, 10:51 PM
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Originally Posted by Clon3 View Post
Just doesn't make sense to me that a simple battery change would "require" a full ECU reflash just for the car to know how to idle properly...
well what I mean is would unplugging my battery for extensive periods of time throw off the tuned settings on any of my reflashed maps?? thats what worries me.
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Old 01-18-2011, 11:17 PM
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For a tuned/modified ECU.. I can see why a manual recalibration makes sense.

My comment is more referring to the average Z buyer who never modifies their car but has to change a dead battery over the years. It would be ridiculous if you had to manually reset the ECU/idle/throttle position just for changing a dead battery...
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Old 01-19-2011, 06:54 AM
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Originally Posted by Clon3 View Post
For a tuned/modified ECU.. I can see why a manual recalibration makes sense.

My comment is more referring to the average Z buyer who never modifies their car but has to change a dead battery over the years. It would be ridiculous if you had to manually reset the ECU/idle/throttle position just for changing a dead battery...
You don't have to manually reset the ecu. You just have to give it time to adapt and sometimes that can take awhile.
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Old 02-07-2011, 04:12 PM
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Default Same issue

Hey guys. I also have an 03 with 75k miles on it now. I recently purchased a new battery because my old one was dying. I've had the new battery now for two months with no issues. When I started the car while it was already warm today, it bogged down and stalled for the first time. On a cold start it's totally fine. Sometimes it will stall when it's warm, sometimes it will keep afloat but chokes. The car starts beautifully because of my Optima battery. Recently, I replaced my stock head unit and the Service Engine Soon light came on. I reset the ECU to get rid of it (there was nothing to service, my car has had its tranny fluid changed very recently, oil, air filter, coolant flush etc etc.... all the usual stuff). I did this about a week ago..... and so I'm guessing this has kinda screwed with the idle.

Do I also leave this alone???? Is the ecu recalibrating itself because I reset it a week ago? Clon, is yours still doing it? It was 100% fine before this afternoon so.....
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Old 01-23-2013, 12:40 PM
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I have the same exact problem as well I have 03 350z manual and I have disconnected the batteries because I was installing subs in it. It was working fine first times I disconnected the batteries but last time I had to disconnect it because I was fixing my sub box so I had to take everything out. The day after I already had connected the battery my car started to stall on hot starts I am not sure if disconnecting and connecting the battery so much that it causes this problem. It turns on normally on cold starts but on hot starts It dies unless I rev it up a little bit and it starts to idle fine. Anyone know how to fix this?
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Old 01-23-2013, 08:09 PM
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Eventually it ECU will just calibrate itself. It takes anywhere between 2-4 weeks to be fully back to normal. I disconnect my battery as least once a year for vacations...
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Old 01-24-2013, 05:36 AM
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Thanks for reviving this thread. I have the same problem and didnt really know how to describe it without making it look like something else .

Glad to know its "normal".
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Old 01-24-2013, 09:14 AM
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So let me get it right... It is normal to have your 350z die on you only on hot start and start up find on cold start? and what you have to do is just wait for the ECU to recalibrate and it will start up correctly? correct me if im wrong thank you!
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Old 01-24-2013, 08:49 PM
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sounds about right.... just give it some time.. ECU will eventually recalibrate itself.. takes a while tho...
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Old 01-24-2013, 08:52 PM
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ok sweet well im glad to know that Its not a serious problem and its a self fix haha.. do you know if theres anyway I could do to just fix it by hand or a way to do it quickly?
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