I seem to have an electrical fault in my Proton M21 that I can?t pin point. 

For some reason when I stop at a set of lights or something similar
the head lights dip pretty badly and the electrical devises like the
radio in the car dim and sometimes flicker as well. This does not
happen all the time, but most. The car has stalled a couple of times
while stopped. As soon as I put my foot on the accelerator, up the
revs, and hold the car steady with the break, everything seems to
brighten up again, till I stop revving again, so it only really
happens when the car is idling. The problem is much worse when I?m
using the air conditioning or using the electric windows, in fact when
I stop the car and it?s in idle I turn everything off.

Also some reason this problem SEEMS to be worse when there is moisture
in the air. I live in Queensland, Australia and it can get really
humid which does not help.

I replaced the battery and this did not help and I?ve had the
alternator checked several times and each time it is charging up
perfectly.  I?ve called several auto-electricians and none of them
seem to be able to offer much in the way of advice.

Can anybody out there diagnose this issue and let me know what I need
to do to get it fixed. It?s driving me nuts !! Have I bought a dud ?

If you need any further information, do not hesitate in contacting me.

Many thanks.

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Request for Question Clarification by redhoss-ga on 28 May 2006 05:51 PDT

Does the battery go dead if you don't drive the car daily.

It sounds like a faulty batter, alternator or regulator

- best get all three checked

If there is nothing wrong with your alternator, then you probably have
a short somewhere. I had a similar problem and isolated the circuit
with the short by removing fuses one at a time until I found the bad
one. The fact that the problem gets worse when the humidity is higher
makes sense if it is a short.

It sounds to me like your idle is set too low.  This would also result
in stalling.  This seems especially likely since you seem to have
already checked the alternator output.

I'm not familiar with the Proton: they don't import them into the
U.S., however I'm assuming it is computer controlled fuel injection. 
Your idle may be adjusted with a bypass screw in the throttle body, or
it may not be adjustable.

If it is not adjustable, you may have a problem with either the
throttle position sensor or the idle speed control motor.   Low idle
can also be caused by carbon buildup in the throttle body.

Even a perfect alternator cannot provide enough power if it isn't
turned at a sufficient RPM.

I have written several articles which tell more about computer engine
controls, alternators, and batteries.  They might be of help to you.
They are:

http://econofix.com/computer.html
http://econofix.com/alt.html
http://econofix.com/battery.html

I am assuming that when you idle the engine up a little bit the lights
get normally bright and the accessories work "up to speed".

Of course if you have a carburettor youcan just set theidle up a bit.

This should fix your problem.