There is a diaphragm at the carburettor which is meant to increase the idle
speed when electrical load is applied. The vacuum going to the diaphragm is
turned on/off by a "three way solenoid". On another car I looked at, with
the exact same setup, 12VDC is applied to the solenoid when the air
conditioner is on. That allows vacuum into the idle diaphragm, increasing
the idle speed. On the faulty car, 12 VDC is applied constantly, but no
vacuum is applied to the diaphragm. At least now I know what the problem is.
All I have to do is understand how that dratted valve is supposed to work,
and what activates it.

Anyway, this may be a more appropriate question for a motoring newsgroup, so
sorry for the diversion.

Henry

"Bob Minchin" wrote in message
...
rednelb wrote:

ALTERNATOR!!! Seems like it's going bad slowly. Cheap and easy fix!

"Henry Mydlarz" wrote in message
...
My daughter has an old 1.3 litre engine Ford Laser. The idle speed is
normal
until the headlights are turned on. Then it drops by about 20%. When
the
brake lights come on there is a further drop in idle speed, until the
engine
occasionally stalls. Having dabbled in car engine repair and car
electronic
repair I have never come across this. Can this be an alternator
problem
where it puts too much load on the engine under heavy current? If so,
what
would it be about the alternator that would cause this? Can it be a
non-electrical problem?

Thanks for any advice.

Henry.



Why should it be the alternator? A failing alternator would generate less
power
and put less load on the engine surely?
I'd suspect the timing and or carburator settings. The OP did not say if
the car
runs ok in normal driving.

Bob in UK