Hi Everyone,

New to the forum and looking for some help with an issue my wife's parent's 2002 Magna VR-X has just started having. Some back-story possibly related to the issue, I installed a new head unit for them this Sunday just gone and in thinking back over the process the next day in trying to nut out why there were two blown fuses at the end of the install, I realised I didn't disconnect the battery while cutting of the old radio unit plug :facepalm. So obviously I have connected various wires to the constant 12v battery wire through the steel head of the side cutters, resulting in two blown fuses required for the radio system (I did disconnect the battery later on when stripping the wires but that's beside the point now :P).

I think at the same time that the fuses blew, it has also caused some other electrical issue as the next night when driving it back to the inlaw's house, whenever coming to a near or actual complete stop at most intersections it seemed to dip in revs and the battery light would flash for a bit before stabilising back at normal idle RPM but a couple of times it actually full on stalled. Before the install for its whole life previously, the car has NEVER had any issues whatsoever, let alone of this nature. The issue continued to occur a couple more times today and testing later this afternoon it seemed the car had to fully warmed up (say after driving for 10min or more) till the issue started showing up.

So does anyone have any clue what the issue could possibly be? My wife said that the TCL light flashed up as well during one instance of this issue and she was just pulling slowly into a park at the service station. I am thinking the only wire in the main radio plug loom capable of doing some damage with 12v connected to it is the ignition feed, maybe damaging the ignition module...but how could this be affecting the idle of the car? The problem literally only surfaces when slowing to low enough revs for the idle control to take over, so stopping for an intersection or very slowing pulling into the garage, which is downhill and so it was pretty much idling down to a stop.

Cheers,

Craig

Whenever you disconnect the battery the car needs to relearn the idle. Just let it idle in the driveway for 5 - 10 mins and it should be right.

Are you serious that's all it is?? I did have to set the car model and engine size after reconnecting the battery, I would not think resetting the ECU would have this kind of effect though. Fair enough it has to relearn your driving style but for it to actually full on stall every 3rd-4th intersection because it's still learning it's own idle? That doesn't sound right to me...

Check and double check all fuses. Check battery terminal connections. Check your ground wires.

Are you serious that's all it is?? I did have to set the car model and engine size after reconnecting the battery, I would not think resetting the ECU would have this kind of effect though. Fair enough it has to relearn your driving style but for it to actually full on stall every 3rd-4th intersection because it's still learning it's own idle? That doesn't sound right to me...

That's not true.

Are you serious that's all it is?? I did have to set the car model and engine size after reconnecting the battery, I would not think resetting the ECU would have this kind of effect though. Fair enough it has to relearn your driving style but for it to actually full on stall every 3rd-4th intersection because it's still learning it's own idle? That doesn't sound right to me...

Yep. Disconnected the battery on my TL when doing the cam belt, refused to idle after that - would cut out while driving whenever it came to a stop. Parked it at home, I had to keep my foot on the accelerator to keep it from stalling, did this for some 10 minutes testing the idle speed by lifting off the accelerator gently every now and then. Eventually came good. ECU and ISC communication seems very slow for some reason.
Wife's Lancer (2004) does the opposite after disconnecting the battery, idle goes up to 2,000 rpm even when hot and slowly settles back to normal.

Meh. As long as you know about that and get the idle right before you drive it on the road, no problem really. Driving while the idle is poor is dangerous, lift off in a slow corner, stall, no power steering. Almost took out the letterbox coming up the driveway doing that. lol

PS "Relearning your driving style" is a gearbox function, little to do with the engine management.
Nothing to do with you cutting wires and blowing fuses, fortunately.

Check and double check all fuses. Check battery terminal connections. Check your ground wires.

Will check the fuses, but I don't see how a blown fuse would cause intermittent idle problems. Battery terminals are definitely tight, if nothing else works I might try a different ground point for the new head unit (I am guessing this is what you were referring to on your comment about ground wires?).


That's not true.

What is not true? Sorry but your statement in reply to my post is way to unspecific to draw a conclusive meaning from it.


Yep. Disconnected the battery on my TL when doing the cam belt, refused to idle after that - would cut out while driving whenever it came to a stop. Parked it at home, I had to keep my foot on the accelerator to keep it from stalling, did this for some 10 minutes testing the idle speed by lifting off the accelerator gently every now and then. Eventually came good. ECU and ISC communication seems very slow for some reason.
Wife's Lancer (2004) does the opposite after disconnecting the battery, idle goes up to 2,000 rpm even when hot and slowly settles back to normal.

Meh. As long as you know about that and get the idle right before you drive it on the road, no problem really. Driving while the idle is poor is dangerous, lift off in a slow corner, stall, no power steering. Almost took out the letterbox coming up the driveway doing that. lol

PS "Relearning your driving style" is a gearbox function, little to do with the engine management.
Nothing to do with you cutting wires and blowing fuses, fortunately.

I'll give it a shot, still doesn't sound right to me...it feels more like I've done damage to some engine governing electrical component.

Yes it is dangerous, my wife was supposed to drive it a couple of hours down to Melbourne to pick up her parents from the airport...I ended up leaving work early and driving her down myself in my car just to be safe.

I've owned a couple of R31 skylines in the past and the ECU for these after a full reset would always go through an initial learning process that adjusted fuel and ignition maps from the base default map to optimise fuel efficiency and power delivery and this process would continuously be going on afterwards as well but at a much slower rate once everything averaged out until the next reset. I would think this is still a feature in car ECUs of this day an age, as my R31's were pre-1990 and it was a relatively "new" feature back then? Obviously this has nothing to do with my current issue though, I was just commenting about it when the comment was made that the ECU has to relearn the engine idle which just sounds silly to me...once the engine specification is set (3.5L or 3.0L), there should simply be a default idle rpm it sits at that the engine is designed to run at during idle.

Anyway will advise the inlaws to try this and report back.

Cheers,

Craig

My TE never had the problem, but my 2002 VR-X does as you've described. The car will likely stall instead of idle when first started after the battery has been disconnected. When I had the battery replaced I had to hold the throttle open a bit at intersections to stop it from stalling (easy to do in a manual). By the time I got home it was able to idle. Since then, if I disconnect the battery for any reason, I let the car idle for 5 mins with and without climate control on before driving. Once it has learned how to idle again it's fine.

My TE never had the problem, but my 2002 VR-X does as you've described. The car will likely stall instead of idle when first started after the battery has been disconnected. When I had the battery replaced I had to hold the throttle open a bit at intersections to stop it from stalling (easy to do in a manual). By the time I got home it was able to idle. Since then, if I disconnect the battery for any reason, I let the car idle for 5 mins with and without climate control on before driving. Once it has learned how to idle again it's fine.

As before, my TL does that. BUT my TJ doesn't, nor did my TS V6 or 4 cylinder. Go figure.

I've owned a couple of R31 skylines in the past and the ECU for these after a full reset would always go through an initial learning process that adjusted fuel and ignition maps from the base default map to optimise fuel efficiency and power delivery and this process would continuously be going on afterwards as well but at a much slower rate once everything averaged out until the next reset. I would think this is still a feature in car ECUs of this day an age, as my R31's were pre-1990 and it was a relatively "new" feature back then? Obviously this has nothing to do with my current issue though, I was just commenting about it when the comment was made that the ECU has to relearn the engine idle which just sounds silly to me...once the engine specification is set (3.5L or 3.0L), there should simply be a default idle rpm it sits at that the engine is designed to run at during idle.


What you describe there is the normal process every ECU goes through when you start the car, base maps are used then modified according to sensor input. Happens every time you start the car, not just after a battery disconnect.
I doubt if an ECU modifies maps and retains the info for the next time you start the car, but someone can flame me if that is not correct. lol

Default idle is set in the ECU maps but it just takes time for the ECU to get the ISC in the right spot. For some cars at least.

There are two sets of engine quantities these ECUs have to re-establish after losing power supply: fuel trims and idle speed control position.

The fuel trims (idle, mid, high) are based on feedback from the oxygen sensor (which is only monitored after the engine is close to normal operating temperatures), and how close the default trims are to being correct for any particular engine can depend on a number of factors including:
- how close the injectors are to the nominal parameters (flow/latency) set in the ECU;
- how close the fuel pressure regulator is to spec;
- how close the MAF is to spec;
- how close the oxygen sensor is to spec;
to name some.

I've logged the process of re-establishing the idle fuel trim, and with a warmed up engine in my car it usually takes at least 4 minutes of idling for the first update to be logged, and another minute or two for the follow-up update that gets the trim quite close to its long term average.

The idle speed controller adjustment also needs to be re-established; if the base engine mixture is far from nominal due to variance in the above components, the engine will run poorly and unevenly making the idle speed adjustment take longer to establish.

While I'm sure some cars have components in good condition that combine to result in a very poor initial running condition (due to manufacturing variation), most cars should be expected to start and idle from a battery disconnection without stalls. Many will be driveable without waiting for the trims and idle speed to be re-established, but not all.

If a car isn't driveable after a battery reset until it has "relearned" it may be worth giving the intake, fuel delivery and ignition systems some attention. However, manufacturing variation may well mean that some engines just need the ECU to be given the time required establish the optimal running settings, and as long as the engine runs well after the relearning is done it has to be accepted unless you want to spend $$$ to try and improve the situation.

There are two sets of engine quantities these ECUs have to re-establish after losing power supply: fuel trims and idle speed control position.

The fuel trims (idle, mid, high) are based on feedback from the oxygen sensor (which is only monitored after the engine is close to normal operating temperatures), and how close the default trims are to being correct for any particular engine can depend on a number of factors including:
- how close the injectors are to the nominal parameters (flow/latency) set in the ECU;
- how close the fuel pressure regulator is to spec;
- how close the MAF is to spec;
- how close the oxygen sensor is to spec;
to name some.

I've logged the process of re-establishing the idle fuel trim, and with a warmed up engine in my car it usually takes at least 4 minutes of idling for the first update to be logged, and another minute or two for the follow-up update that gets the trim quite close to its long term average.

The idle speed controller adjustment also needs to be re-established; if the base engine mixture is far from nominal due to variance in the above components, the engine will run poorly and unevenly making the idle speed adjustment take longer to establish.

While I'm sure some cars have components in good condition that combine to result in a very poor initial running condition (due to manufacturing variation), most cars should be expected to start and idle from a battery disconnection without stalls. Many will be driveable without waiting for the trims and idle speed to be re-established, but not all.

If a car isn't driveable after a battery reset until it has "relearned" it may be worth giving the intake, fuel delivery and ignition systems some attention. However, manufacturing variation may well mean that some engines just need the ECU to be given the time required establish the optimal running settings, and as long as the engine runs well after the relearning is done it has to be accepted unless you want to spend $$$ to try and improve the situation.

Good info! Thanks for that.

Should of Bought this... (http://www.supercheapauto.com.au/online-store/products/Aerpro-Wiring-Harness-APP0111-to-suit-most-Mitsubishi-1-plug-type.aspx?pid=224821&menuFrom=110601#Description)

There are two sets of engine quantities these ECUs have to re-establish after losing power supply: fuel trims and idle speed control position.

The fuel trims (idle, mid, high) are based on feedback from the oxygen sensor (which is only monitored after the engine is close to normal operating temperatures), and how close the default trims are to being correct for any particular engine can depend on a number of factors including:
- how close the injectors are to the nominal parameters (flow/latency) set in the ECU;
- how close the fuel pressure regulator is to spec;
- how close the MAF is to spec;
- how close the oxygen sensor is to spec;
to name some.

I've logged the process of re-establishing the idle fuel trim, and with a warmed up engine in my car it usually takes at least 4 minutes of idling for the first update to be logged, and another minute or two for the follow-up update that gets the trim quite close to its long term average.

The idle speed controller adjustment also needs to be re-established; if the base engine mixture is far from nominal due to variance in the above components, the engine will run poorly and unevenly making the idle speed adjustment take longer to establish.

While I'm sure some cars have components in good condition that combine to result in a very poor initial running condition (due to manufacturing variation), most cars should be expected to start and idle from a battery disconnection without stalls. Many will be driveable without waiting for the trims and idle speed to be re-established, but not all.

If a car isn't driveable after a battery reset until it has "relearned" it may be worth giving the intake, fuel delivery and ignition systems some attention. However, manufacturing variation may well mean that some engines just need the ECU to be given the time required establish the optimal running settings, and as long as the engine runs well after the relearning is done it has to be accepted unless you want to spend $$$ to try and improve the situation.

Wow! Thanks for the great informative post!


Should of Bought this... (http://www.supercheapauto.com.au/online-store/products/Aerpro-Wiring-Harness-APP0111-to-suit-most-Mitsubishi-1-plug-type.aspx?pid=224821&menuFrom=110601#Description)

Thanks but that doesn't look like the right plugs at all for the head unit.
__________________________________________________

Well everyone, it turns out all of you who said the idle had to be re-learnt by the ECU (pretty much everyone :P) were right. It seemed to already be occurring less when I last drove it and after my father in law tried as suggested (5min at idle, 5min at climate control on idle), he hasn't seen the issue surface at all since.

Thank you very much everyone for posting your advice so quick and informatively :thumbsup:. If I ever happened to buy a Magna this would definitely be the forum of choice for me :happy:

Cheers and thanks again,

Craig

The idle should reset itself properly the first time you drive it. If this was an ongoing issue then there would seem to be something more to it. Good that its working properly now but I have never seen such an issue repeat itself after the first drive. In fact, I have only seen the idle play up once in a tj after disconnecting the battery.

Should of Bought this... (http://www.supercheapauto.com.au/online-store/products/Aerpro-Wiring-Harness-APP0111-to-suit-most-Mitsubishi-1-plug-type.aspx?pid=224821&menuFrom=110601#Description)

thanks mate great info, i bookmarked it for later