Higher RPM = alternator turning faster = higher voltage. Lower RPM = alternator turning slower = lower voltage. If you're idling and rev higher and hold it does the voltage go up and drop again when you let off the accelerator?

Given your symptoms, it may possibly be just the voltage regulator. Those can be replaced as an individual component, but if it's the problem I'd just go ahead and replace the whole alternator as a unit.

I am not an expert at this, but that's what I think.

 

Yup i get that, but my thoughts were more along the lines of why is the conclusion that his idling issues are voltage caused. With the car running off the battery the exact voltage the alternator is putting out wont matter as far as the engine is concerned. As long as the battery is charged its going to put out a mostly steady 12v.

Unless i read wrong and the issue is actually the voltage not the car idling and almost stalling when coming to a stop?

 

Voltage drops when the vehicle almost stalls.

 

So if the engine rpms drop from almost stalling the alternator has also lost rpms and wont be providing the same voltage to the system and battery while the battery is under the same current draw. That situation will always result in lower voltage readings.

Im just wondering why when the first time you came to a stop and experienced the car almost stalling you went down the road of it being a voltage issue? Usually when a car wants to stall its because its not getting enough air or fuel or theres something wrong with the ignition system like a weak coil pack or fouling spark plugs.

 

Bouncing ideas off my buddy. He had the same issue on him m5. Ended up being his alternator.

I mean even when the car is not attempting to stall, the volts are low, driving on the highway etc. The volts are constantly low.

At 57k a spark plug or coil pack shouldn't be the issue right? I mean nothing is guaranteed, but...

I could check A/F and see if my maf is an issue? Couldn't low volts with a maf and it's readings?


Anyway emailed my advisor and trying to get the car in Friday.

 

If a low voltage situation at stop was causing stall conditions and you're also getting low voltage all the time as you just indicated then you'd be in a constant state of almost stalling.

Have you checked your odb codes? You may not have a cel, but most cars will pop pending codes before an actual code is thrown. Im not sure alt/batt or not how a stall condition hasn't cuased some sort of code either. You could also check to see if maybe the A/C clutch or something else in the belt system is hanging up. If somethings too tight or binding enough it could drag and maybe cause this issue. Something like that wouldn't trigger an odb code. I still think though theres something up with the air or fuel like a bad throttle body or something.

My wife had a 9-5 saab that had a bad throttle body that did exactly this. It didnt stall everytime, but when it did it was always slowing down and stopping. We got rid of the car before i could resolve the problem.

 

I've checked for codes and nothing :/ mind you using the torque app. Ive got an appointment a week from Friday to bring her back in. I have NOT done a throttle body reset. Guess I'll leave that to the dealer to figure out.

Regardless there is a problem, any advise of the dealer says there isn't a problem?

 

I would expect them to say theres nothing wrong since there arent any codes. If you can do a test drive with a tech and replicate the stalling then they should attempt diagnosis beyond pulling it in and checking the codes. My main advice is to not mention anything about the voltage and just explain and demonstrate the stalling. If you tell them it's voltage related then they wil only check the electric system and see everything is within spec and send you on your way.