1.9D low revs on start, and revs can be controlled with the headlights switch.

[chiefwhosm]

Hi,
    I'm trying to get my golf back on the road but I'm having a bit of an odd issue. Basically I first thought it was the aux belt as what happens is that on starting the engine you get a very nasty squealing sound from the aux belt area under the bonnet. If you accelerate the sound gets much worse. I know water pumps can also make quite a racket when they go and also wondered if it could be that. The odd thing is that after a few minutes the sound goes away completely and the engine bay sounded just as it should.
Today however I spotted that when you start the engine the rev counter sits at 6 and stays there, you can accelerate all you want but the needle never moves, all the while with the squeal. As the squeal lessens so the needle climbs until it reaches the correct idle of around 10 and the sound goes completely. Strangest still is that if I use the head light switch, then my revs drop again, sidelights 8 revs, full beam 6 revs as though battery power holds the key, but while I admit my mechanical knowledge is pretty poor, I didn't,t think the battery was needed by the engine once the engine had fired.
Any suggestions as to why this seems to be so? Could it be the alternator?
Thanks for any help/advice you can give,
Chief.

[Bellend]

Any lights on the dash i.e battery?

Could be a wiring/earth issue.

[chiefwhosm]

Hi,
    Nope nothing else out of place, I should have mentioned (forgot all about it) that all this started when for the first time ever I started the car without waiting on the glow plug dash light going out. I'd only just stopped the engine so I knew they should still be hot. Could have been coincidence of course. I just find it strange that it rights itself after a few minutes, but if you then stop the engine and start it it returns to the low revs etc again. I don't mind taking the battery out and charging it to see if it makes a difference, as I said it was only today I found any connection between using the battery and the revs dropping.
Chief.

[javalin]

>I didn't,t think the battery was needed by the engine once the engine had fired.
yes there is, battery acts as a "damper" to regulate the voltage from the alternator which produces ~19v when unloaded.

[chiefwhosm]

Charged up the battery, put it in, started the engine and the dash went dead. This does happen with this car if the connections aren't quite tight. One odd thing that did happen on the second attempt was on switching on the ignition the temp, oil, battery, glow plugs and handbrake lights rapidly flickered, not full brightness just dim lit/unlit.
After taking the negative lead off and putting it back on again after several attempts (it is a but cold here) the engine stopped stalling and started running, though at 4 rpm on the counter and with the squeal, which as mentioned before eventually stopped when the counter moved up, to just under the 10.
Headlight switch didn't appear to affect the revs today.
Chief.

[javalin]

ignition switch fault maybe?

[benjy_b]

I'd say you have an alternator fault.

With extra load on the alternator, the revs are dropping. Take the alternator belt off and start the engine, see if the noises go.