> My daughter has an old Ford Laser 1.3l which has this problem. With the idle
> speed on normal, it drops by 20% when the headlights are turned on, then a
> further 5% when the brake lights come on. Then, unless I adjust the idle
> speed way up, the car stalls.
> I found that the diaphragm which compensates for electrical load difference
> by increasing the idle speed is not operating. There is a "three way
> solenoid" which controls the vacuum supplied to the diaphragm. On another
> car it has 12VDC applied to it when an electrical load is turned on. On the
> Laser it has 12VDC on it all the time. Trouble is that although it allows
> free vacuum passing through it, the vacuum also escapes from the vent on the
> valve and does not operate the diaphragm.
> Does anyone here know how this valve is meant to operate? The car wiring
> diagram mentions the solenoid being driven by an "engine speed control". I
> have no idea where that is.
> Any advice will be most appreciated.
> Thank you.
I realize that this is a completely unrelated car and possibly system,
but might give you a new way of looking at what you have. I was just
working on an old R2 (supercharged) Studebaker yesterday and on most of
the '63-64 performance models there was a vacuum-operated dashpot on the
front of the carb. How it would work is like this, you adjust the carb
with the dashpot removed, then install it and start the engine. The
dashpot pulls in immediately when vacuum is applied to it and the end of
it should be adjusted so that it is just off the throttle linkage - i.e.
the linkage is resting against the hard idle speed stop. But if vacuum
drops, as if the car is going to stall or is idling low for some reason,
the plunger in the dashpot will kick out and return the engine to idle.
I suppose that this setup could also be adjusted to allow for fully
closed throttle plates on overrun to save fuel - not sure if that's a
good idea or not. would probably make for a lumpy idle as the dashpot
would constantly be wavering back and forth. But now I'm not being
helpful, I'm just thinking out loud (with my fingers?)
In your specific case, if you're losing vacuum through a vent, I suspect
that you need a new vacuum actuator - sounds like a cracked diaphragm.