Looking to sense check something. I've got a 1994 Discovery 1 with the 14CUX EFI system.

I've noticed when I turn on the headlights (i.e. sort of a moderate electrical load) at idle, the idle speed will "blip" down for a second or two and then come back up to normal (e.g. 750rpm).

It feels like the stepper motor needs to adjust to the increase in load from the alternator to accommodate the current draw.

However. Today I was doing some check-outs in prep for an off road weekend and when I was either winching line in and out (not under heavy forces) or when I ran my onboard compressor, the idle behaved pretty badly. Swinging down to ~500rpm or perhaps even less while under electrical load, then coming back up to ~900rpm after the load is stopped. It settles back down eventually to normal.

Alternator is maybe ~1 year old. Bought from Atlantic British. Standard 100A unit.

What are the group's thoughts on:
1) If this is just what I should expect from a standard alternator + and an EFI system that is not the most refined
2) If this is a signal the alternator perhaps is on its way out

I've winched off road before, but typically have the engine running at higher rpms since I'm actually driving out of an obstacle while winching. When I've done small stuff like winched out small shrubs I typically have the engine off I think.

I have an extra alternator I can pack for the trip - just not sure if perhaps it would be prudent to change now...

 

Maybe just a sign the IACV or base idle passage need a good cleaning. Sounds like the alternator is working like it is supposed to. Maybe check PCV items too, and fuel pressure regulator.

 

Thanks JohnZo - new fuel pressure reguator and IACV and just had the intake cleaned + new vac lines. She idles well otherwise, just the loading that sets it off.
Will probably aim to keep the RPMs up if I do have to use the winch. Will come back if I learn anything else!

 

How old is your battery? Is it's capacity good enough?

Prior to my alternator failing, on the 94, the battery dash light would fade in and out. I was very dim and could only be noticed in the dark. The truck ran fine. When the alternator finally failed, the tach quit and the battery light was bright. Maybe not related to your situation. Perhaps the local auto parts store has an electrical system tester to check out the alternator.

I was thinking about this and decided I would do a base idle check. It may be the previous work moved a crumb around in the passage. Simple to do by plugging the IACV path. Should be 500 -525 rpm (I use the truck's tach). If it dies, then the base idle screw (under a factory aluminum cap) needs to let more air through.