Idling Not What It Was!

[lagonda 42]

Yes, done a search, hoping to narrow things down.

 

I rebuilt the engine and set everything up fine in 2007. Since then, it's idled beautifully, at around 800rpm. More recently, the idling speed has slowly dropped. 500rpm now, and it just hangs in there, but it's more likely to drop lower and stall. It isn't running evenly at anything below 1200rpm.

 

I've also noticed that, on starting, it immediately runs at around 700rpm, very quickly down to 500. Previously, it started at around 800 rpm, revs quickly rising to around 1400, then reducing to 800 as it warmed up. So it's stopped doing the rise to 1400....does that narrow things down?

 

I've swapped the distributor cap and all leads, and ignition ampilfier. Just taken throttle body off, but it seems surprisingly clean. I'll clean it up now it's off, but from the look of it, doubt that it's the problem. Temperature has no bearing on this; other than it's unlikely to stall for literally the first minute from starting, it's the same hot or cold.

 

Slightly off topic, I changed the AFM a few months ago (don't think it's the AFM as I had hoped that the replacement would resolve this as well as the cutting out....cured the cutting out, but idling continued to worsen). The mixture setting on my original AFM was correct; this one I don't think is far out, but I'd prefer to reset it. Can I do this by screwing my original AFM's adjustment all the way in, counting number of turns, then resetting the replacement AFM's screw to the identical setting?

[Tom Fenton 1,542]

If the idle isn't behaving when cold then I'd look at the SAD first (cold idle valve). The aperture is small and prone to getting gunked up.

As for your AFM method, it won't work as they won't be all the same. Only reliable way to set it up for idle mixture is on a gas analyser.

[lagonda 42]

Hi Tom,

Yes, I suspect SAD has a problem, but had read that it's unlikely to affect idling issues. Did clean and reset it back in 2007, but that is 60,000 miles ago, so I'll do that next.

 

I thought that might be the case with the AFM, still, worth asking!

[lagonda 42]

Took the SAD off it & cleand it up, tested, all working OK. One of the nearby water hoses was weeping slightly, so not a complete waste of time.

 

Think I've found the culprit, though. Sucked the rubber tube going to the distributor vacuum unit....and the diaphragm in that has failed....so it's been sucking unmetered air into the throttle body, and of course, no vacuum retard for the ignition timing.

 

Are these vacuum units reasonably available still? Annoyingly I have a spare distributor, but the vacuum unit on that leaks as well.

[iPlod999 143 1 Cars]

http://www.h-h-ignitionsolutions.co.uk/

 

These guys provided a reconditioning service. £25 if I remember.

[lagonda 42]

Been searching, and it seems I can buy a new vacuum capsule, Bosch 1 237 123 027, over here in France for around €46, equating to about £32.50, which seems roughly £6 cheaper than UK prices. P&P on top, but I'll also be buying a new Bosch ignition amplifier, which works out at about £22. Would have thought the ignition amp would be dearer than the capsule, but can't complain, pleased both parts available still.

[Anthony 1,003]

That sounds very cheap for a genuine Bosch amp!

[lagonda 42]

Yes, strangely they want double that for a Valeo one. I see they can also supply new AFMs, but they are €568, around £400.