SD33 blowing white smoke at idle when warm

[AussieRuss]

Hi everyone, newbie to the forum here, I have a problem I'm hoping you can help with.

I have a 1987 nissan patrol ute with the SD33 Diesel engine that we have owned since new. It's always been a good ute, but in the last 18 months or so, it's developed this annoying fault that I can't fix.

It starts and runs fine when cold, but once it warms up, it idles at about 1500 to 1800 rpm and blows white smoke. It sounds like the injector pump is overfueling.

I've checked all the vacuum lines to and from the injection pump to the throttle body, and they are fine. Is there a cold advance on these pumps?

Any ideas will be greatly received!