Pulsing Idle

[crickleymal]

1.9D DW engine. When I start the engine in the morning (i.e. when the engine is cold) it's taken to pulsing the idle. It's ok for the first few seconds but as soon as I apply any revs the idle goes erratic. It revs up to 1200rpm then drops to nearly 800 then back up to 1200 and so on. It's a very regular pulse though takes about 1.5 seconds to complete a cycle. Once the engine is up to temperature it's fine and remains fine all day.

Any ideas please?

[Ol'Jeffers]

Air leak at the inlet (manifold?) on the injector side? Possibly.

[crickleymal]

Ok so what do I do to find out if that is the case?

[Ol'Jeffers]

At this point I have to hold my hand up and say that maybe Rustscrat or one of the other extremely knowledgeable guys here will know.
If it was a normally aspirated petrol engine then I'd know but these diesels are foreign to me......sorry! :S

[Romahomepete]

At this point I have to hold my hand up and say that maybe Rustcrat or one of the other extremely knowledgeable guys here will know.
If it was a normally aspirated petrol engine then I'd know but these diesels are foreign to me......sorry! :S

Ther is some kind of device that increases the engine revs at idle when cold, I presume controlled by some kind of sensor.

I would start there.

Peter

[crickleymal]

Ther is some kind of device that increases the engine revs at idle when cold, I presume controlled by some kind of sensor.

That was my thought but I don't know where the sensor is.

[brodfather11]

Air leak at the inlet (manifold?) on the injector side? Possibly.

You can discount the air leak at Injector side as the older engines do not need an airtight seal between manifold and cylinder head to run.
The older 1.9 has a thermostatic controlled cold start lever on the fuel pump. There are a lot of posts about it and how to check and adjust.

The newer type rely on elctronics to monitor coolant temp. etc to ensure low emissions. An air leak at the manifold could upset the airflow meter and also the E.C.U. tudy:

[crickleymal]

It's the later DW engine(54 reg) so all electronic control I assume.
A bit more info. When you start the engine from cold it will idle fine until you take some power from the engine. Say you twitch the steering, the power steering takes some power and this sets of the pulsing. Likewise it will idle fine until you rev the engine then it will start pulsing.
I'll have to investigate at the weekend.

[crickleymal]

I'm going to mark this as solved. I found a pipe that goes from the airbox to the front grill had come loose. It's a pipe with several longitudinal slits in it. Put it back in place and the problem seems to have gone away. Seems a bit unlikely to me but hey ho.

I also had a look at the fuel injection controller thingummyjug. It's mechanical control (much to my surprise). I gave everything that moved on it a lube with some Triflow silicone/ptfe lubricant.