alternator diagnostic: insufficient output current at idle

[enry]

I have a 2003 MSP, if I idle at warm and headlights and AC fan on, 15 amps are pulled FROM the battery, which means, eventually, it will die on its own when the battery is discharged.

I have to stay over 2000RPM for the alternator to generate the required current. However, my idle at warm is 500RPM whether lamps+AC fan are off or on.

Sometimes, when I am at 3000RPM and driving, if I go to neutral and let go of the gas, the car will stall.

Here's what I've checked so far:

ALTERNATOR OUTPUT CURRENT
40amps if over 2000RPM.
BATTERY CHARGING CURRENT
+10 over 2000RPM with lights+ac fan on
-20 at 500RPM (warm idle) with lights+ac fan on
BATTERY
The battery is good, no dried up elements, it seems it can hold a charge.
When charged, 12VDC with engine off. With engine on, 14VDC when over 2000RPM, decreases rapidly if idling and with accessories on.
BELT
The belt that feeds the alternator feeds the AC and vacuum pump, and both AC, power steering and power brakes work fine. No horrible belt slipping noises.
SPARK PLUGS
clean and properly gapped

This seems to me not normal behavior. Is it possible that the alternator is putting out insufficient current
Or, should the PCM be smart enough to compensate for current draw (or battery voltage < 14V) and increase the idle RPM automatically ?

The service manual chapter on the generator is BS, and only says that the alternator should put out more than 0 Amps. Wow, thanks, I had no idea.

The following issues in the symptom troubleshooting section of the service manual look interesting:

NO.5 ENGINE STALLS-AFTER START/AT IDLE
[FS] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0103B17
NO.10 LOW IDLE/STALLS DURING
DECELERATION [FS]. . . . . . . . . . . . . . 0103B26
NO.11 ENGINE STALLS/QUITS, ENGINE RUNS
ROUGH, MISSES, BUCK/JERK, HESITATION/
STUMBLE, SURGES [FS]. . . . . . . . . . . 0103B28

Should I focus on one in particular?

 

[Fudgie]

Time for an alternator. Does the battery light come on at all? Check to see if it comes on koeo.

 

[enry]

what's the nominal output for an alternator on an MSP? should it be putting out more than say, 25 amps at 500RPM?

 

[Tom03es]

My best guess would be that the internal voltage regulator took a dump. Time for a new or "new" alternator.

 

[thrilhouse]

I have an 03 MSP, have had similar issues. My car stalls when idling randomly a few days a month.. especially after heavy start stop traffic. When idling stopped at light say I have to keep my foot on the gas or it will die, this goes away usually after 10 minutes of driving and keeping it at 2-3k rpm. I have an aftermarket stereo which has high current draw at times and both shops I've taken it to just blame that and offer no solution for me. I have replaced my alternator with a brand new one and still have the issue. I've been troubleshooting the problem in the forums. Sounds like it could be the fuel pump or vac lines..

 

[Maxx Mazda]

The ECU only allows at the most 70% of the available 80 amps to come out of the alt. in order to achieve better fuel economy I've heard. Try switching to a 626 alternator, they're internally regulated, so the ECU would ahve nothing to do with it.