Diesels struggle to reach idle RPM

[BrettB]

Lately, my diesels(Volvo Penta D1-30) struggle to reach idle RPM on start, they hover around 500rpm and try to stall out. I can get through it by running them up to 2000rpm or so in neutral for about a minute and bring them back down to idle. The rest of the day they run fine when we are cruising around. Once we get in to anchor somewhere, about 25% of the time one of them will drop down to around 500rpm and stall out, when I pull it back to idle and drop the anchor.

Thoughts? As always, thanks in advance.

[Compass790]

Not familiar with yr engines but it sounds like a fuel or air leak issue. Check fuel filters & all the fuel joints for a start. I wrap joins in toilet paper to look for leaks. Are they running fine otherwise? no loss of power? How many hours on them?

[NPCampbell]

I dunno about the stall outs but could the starting issue be bad glow plugs?

[rbk]

When’s the last time the valve clearances were checked?

[SailRedemption]

There's a idle adjustment bolt on the injector pump, make sure the second locking nut didn't back off and your idle screw didn't back out. You may have clogged filters as well. I would check the idle screws first.

[skipperpete]

Is there any chance that this could be an alternator issue and the engines are slightly overloaded at startup? The D1-30 was fitted with a 115 amp alternator and that's a lot to spin at idle.

[meridian28]

Since it’s both engines I would check the filters.

[JPA Cate]

We've had those symptoms twice in the past, with different engines.

One time, it was a clogging up fuel filter; the other, the governer needed an adjustment.

Ann

[Wotname]

Originally Posted by meridian28

Since it’s both engines I would check the filters.

Yes, it is unusual for both engines to have similar faults, check what is common to both and/or has the same mechanic carried out work on both engines recently?

Or have you picked up a load of bad fuel lately?

[Lepke]

RPM is controlled by a governor. When the rpm falls below idle, the governor should supply more fuel. It happens very quickly, even at idle. If both engines are having problems, it's something they share, fuel, fuel lines, filters. The injector pump can get gummed up from bad fuel. If fuel is going to sit, it needs a conditioner. Maintenance isn't just changing filters. I use a conditioner every fueling or manually add and circulate if sitting longer than a few months.
Also could be air in the fuel, or air restriction.