Signum throttle 'pulsing' problem

[DHobbs]

OK, got a problem with the siggy. It's only apparent on warm up, about 70'C. It feels like the throttle is being put on then off, giving a mild pulsing/lurching sensation.
When cold or fully warm, it's fine.
I've tried it with cruise control and without.
It's a 150 CDTi.
I've looked at the field remedy for the 3rd injector, but my engine number is out of it's range, so I assume it's been corrected by the factory.

My fuel filter needs replacing, but can't see why this would show up at certain temperatures.

Any ideas before a trip to Vx?

[bobssignum]

Does this only occur on tick over if so then it is almost certainly the throttle position sensor , they ware at the bottom of the scale ;ie first 25% of throttle position best bet is to have it tech 2ed to see what fault codes show up if its as above then expect to see a p0380 code

[DHobbs]

Don't know if it happens in idle. I'll try tonight. When it happens I'm usually on the dual carriageway, so I'll be carefull. Don't want someone driving into me. Would it be lumpy in idle or smooth if the throtle sensor is duff?

I've looked at the secret menus and there's no fault codes stored. I've even looked at the BC/TC inst values but not sure what I'm looking at .

I can only assume the temperature thing is when the thermostat opens.

[bobssignum]

What is probably basically happening is you have an inbalance between your throttle sensor and the oxygen sensor so one sensor is saying not enough air /fuel mix entering the throttle and the other is saying the opposite hence the surging.
If your throttle sensor was duff your tick over during idle will surge up and down between 475-500 and back to the normal tick over of around 800-825 .if you have the car running in this state remove one of the vacuum hoses ,car should settle back to normal revs.

[DHobbs]

What is probably basically happening is you have an inbalance between your throttle sensor and the oxygen sensor so one sensor is saying not enough air /fuel mix entering the throttle and the other is saying the opposite hence the surging.
If your throttle sensor was duff your tick over during idle will surge up and down between 475-500 and back to the normal tick over of around 800-825 .if you have the car running in this state remove one of the vacuum hoses ,car should settle back to normal revs.

Thanks
I'll give that a try. Maybe if I'm feeling adventurous, I might have a look at the throttle sensor solder joints, read on here that they can have a dry joints.

[DHobbs]

Right, tried it idling and no differnece, normal idle speed. It's only apparent for about a minute, so not much time for diagnosis!

[the-wizard]

have a look at the how 2 for the throttle body, could have oil in the circuit board area or needs the re solder fix!.