Avensis D4D Occasional Rough Idling And Smoke

[Call me Ishmael]

Hello Folks,

I have a 2004 Avensis D4D 2-litre with 125,000 miles on the clock. It has been idling a little rough for the past couple of weeks before it's fully warmed up. Cold starting's fine and smooth idling when hot.

On Sunday morning, it cold-started normally and as we were driving away, there was a mis-fire, the engine revs dropped to a rough idle and wouldn't respond to the throtle. Thick black smoke poured from the exhaust, so I switched off and restarted. It ran fine but the engine management light came on. My mechanic did a diagnostic on it, but no fault codes came up and the engine management light went off again by itself.

Since then, we've had some rough idling when luke-warm and occasional blue smoke which clears itself when you start driving.

There's no shortage of power and good acceleration. Presumably some electronic thing's acting up.

Any ideas?

Thanks.