For a long while now I have a surging -pulsing idle when sitting still. I can watch the voltage meter dip and climb in sync with my RPM needle. My boost needle also fluctuates a bit.

Now, if I have the heater or AC on , and i'm applying the brake coming to a halt at a light (or something) - there is a high chance the car will stall - above 75%,

If I have no accessories on and apply the brake coming to a stop the car will get very close to stalling, but then (usually) will "catch" and smooth out.

If I have nothing on and no brake applied + my e-brake on (which turns off the daytime running lights) I will idle just fine with maybe a blip here or there in the voltage meter, which usually reads 13v at idle and 14+ during driving.

And finally - if my car is cold (1st thing in the morning) - I can have every accessory on plus all 4 of my window rolling up and down and the car's voltage and RPM hold steady with no issues. Only when it starts to warm up - do I have these issues. Alternator? Battery? I do have a lightweight flywheel - problem there?

Any help is appreciated.

Do you have an underdrive pulley in addition to that flywheel? That will reduce alternator output, most noticeably at idle. You should be seeing more than 13V at warm idle with no accessories on, more like 13.5-14. This could be from a weak battery, weak alternator, poor connections or wiring, or any combination thereof.
The reason the voltage is higher after a cold start is that the voltage regulator is thermally compensated, so the lower the temperature under the hood the higher the voltage.
The uneven idle could also have other causes, such as an IAC problem. It may not be only from the electrical system.

I am having a similar problem with my 02 WRX but mine is caused by the head unit and stereo system I recently put in the car. I have the pioneer AVIC-N1 navigation and DVD player with 2 amps, upgraded speakers and a sub. This particular head unit draws a lot of power and since I had everything put in I can't have my car idle for very long. I can watch my volts drop drastically (below 11 sometimes) if I am not moving. I have stalled a few times sitting in traffic because of this. I do notice however that when I put the car in park (I have an automatic) I can have the car running for a lot longer before the volts start to drop slowly. I was told that I should have my alternator re-spun to get a higher output and put in a better battery and see if that helps my problem. I don't know if this is your exact problem but it seems like we have the same symptoms.

It doesn't matter what HU you have, no HU can draw enough current by itself to max out the alternator. Amps maybe, but unless you have them cranked and drawing a constant high current they will only cause voltage drops on peaks, not continously. I'd suggest having both your battery and alternator tested, there may be a problem with one or both.

Do you have an underdrive pulley in addition to that flywheel? That will reduce alternator output, most noticeably at idle. You should be seeing more than 13V at warm idle with no accessories on, more like 13.5-14. This could be from a weak battery, weak alternator, poor connections or wiring, or any combination thereof.
The reason the voltage is higher after a cold start is that the voltage regulator is thermally compensated, so the lower the temperature under the hood the higher the voltage.
The uneven idle could also have other causes, such as an IAC problem. It may not be only from the electrical system.

I do have a Vishnu UPulley in addition.

I had my battery tested at the zone and it checked out according to them.
I cleaned my IACV thing and replaced gasket. I will check wiring, but none of that has been disturbed and I have all factory stereo gear - which leaves the alternator...wonder if I can buy one with ability to return if thats not it??

Thanks Mulder - I am going assume its the alternator for now and replace. It is the original alt. that came from Subaru.

If that's an underdrive pulley you should replace it with a stock (or stock size) one and see what happens. That might be all you need to do.
Don't just replace the alternator based on speculation that it *might* be bad. You could be wasting your money. Electrical parts are usually not returnable so you'd be stuck with it.
Find a shop that can properly test your electrical system and diagnose what is actually wrong.

Idle air control valve sticking?
This would give your symptoms of stalling especially when hot.
ISTR there's a thread on cleaning it on here.

I cleaned my IACV thing and replaced gasket.

John, looks like that's already been accounted for. Also the IAC alone wouldn't account for the lower than normal voltage.

John, looks like that's already been accounted for. Also the IAC alone wouldn't account for the lower than normal voltage.

Missed that bit.
The under voltage is almost certainly due to the crank pulley.
I wouldn't have thought the engine sytems were that sensitive though. 13V is not that low.

Missed that bit.
The under voltage is almost certainly due to the crank pulley.
I wouldn't have thought the engine sytems were that sensitive though. 13V is not that low.

Maybe not that low, but lower than normal on a stock electrical system with no high current accessories running. I'll see around 14V on mine, unless it's really hot outside in which case it is a bit lower.

Thank you guys. I bought the car with the pulley already on it. Would you say that replacing back to stock is a hard install?

I am going to get alternator tested on Thursday.

For a long while now I have a surging -pulsing idle when sitting still. I can watch the voltage meter dip and climb in sync with my RPM needle. My boost needle also fluctuates a bit.

Now, if I have the heater or AC on , and i'm applying the brake coming to a halt at a light (or something) - there is a high chance the car will stall - above 75%,



This really sounds like a symptom of another problem. I highly doubt the car would stall because the alternator was not charging at idle.

1. The battery checked out. That will keep the electrical systems operating at idle even if the alternator is NFG.
2. If you've never had the battery run completely down and not start the car, your alternator must be charging.
3. Underdrive pulley or not, your battery will be charged while driving if the alternator is working at all.
4. You wouldn't be able to load the electrical system enough to cause the alternator to stall the motor if the IAC is operating correctly.

Following this logic, it has to be a sensor, actuator, or mechanical problem with the engine. I'd clean both your MAF and IAC and bet that solves it.

-Steve.

Thanks Steve for the info and opinion.

I am now leaning more toward a tuning issue with my larger than stock injectors being the culprit - which of course changes the topic of this issue.

Alternator ended up checking out ok.

MAF has been swapped out before and cleaned.
By the way, the MAF plug is directly on top of my intake with the harness wires pointing at my headlight. Could placement have an issue here?

MAF has been swapped out before and cleaned.
By the way, the MAF plug is directly on top of my intake with the harness wires pointing at my headlight. Could placement have an issue here?

Hmmm... aftermarket intake? Was the car custom tuned with that in place? Try putting on a stock intake and see what happens.

Have you checked the ECU for historical codes? Did you try resetting the ECU? Probably a good idea to hook up a OBDII logger and read what your fuel trims are doing. I had a very similar problem with stalling when I put my first water injection controller on. It was wired into the MAF which burdened the sensor circuit too much and made the fuel trims max out.

-Steve.

edit: just thought of something else... when was the last time you changed your plugs, or at least looked at them and checked the gap? I recall plugs made a big difference when I had the stalling problem. Even when my fuel trims were freaking out, new plugs made the stalling go away.

Hmmm... aftermarket intake? Was the car custom tuned with that in place? Try putting on a stock intake and see what happens.

Have you checked the ECU for historical codes? Did you try resetting the ECU? Probably a good idea to hook up a OBDII logger and read what your fuel trims are doing. I had a very similar problem with stalling when I put my first water injection controller on. It was wired into the MAF which burdened the sensor circuit too much and made the fuel trims max out.

-Steve.


Yeah -lots of aftermarket parts including intake (bigmaf)

I have reset ECU which actually seems to help for while then its back to the same thing.

I have also read my fuel trims in the past - but its been a while. I forget...if I am reading negative fuel trim numbers do i add fuel or take out? And is the idea to be as close to zero as possible. Thanks!! You may be on to something here.

Yeah -lots of aftermarket parts including intake (bigmaf)

I have reset ECU which actually seems to help for while then its back to the same thing.

I have also read my fuel trims in the past - but its been a while. I forget...if I am reading negative fuel trim numbers do i add fuel or take out? And is the idea to be as close to zero as possible. Thanks!! You may be on to something here.

Don't worry about your fuel trims unless they are maxing out at +25 or -25. If a reset temporarily helps, then there is likely something going on that's causing the fuel trims to go way off when it warms up and learns. What EM are you running? You are tuned for that bigmaf right? If not, bingo!