Disco 2 Td5 - Vibration under (big) load & (high-ish) speed

Hi all, quick question to see if I can narrow down an issue.... Td5 auto, 90K on clock. Runs well, no problems starting, good clean power upon pulling away etc.

On weekend, travelling back to London along the M20, happily rolling along and keeping up with the traffic around 70mph ish... no trailer and just me with a passenger, and the usual Discovery toolkit in the boot, came to the big long drag up the hill from Maidstone. Accelerated a bit at the bottom to give me a good chance to keep going, TC locked, pulling about 2.5k to 2.6k RPM. Noticed a slight vibration, which cleared when off the throttle, accelerated again, then again, vibration. Initially thought it was driveline issue, but then it was co-incident with load, acceleration & speed, so perhaps thinking a miss-fire (OK not on a diesel) but something more engine related (no smoke from tailpipe etc)

Did a search and a couple of things have come up in similar circumstances:

1) Actuator on turbo not moving freely, giving an false signal to ECU and therefore incorrect fueling etc
2) Oily red plug and injector harness.

So - I can check the red plug for oil - and clean / replace as may be necessary. I have previously checked the actuator rod on the turbo (mole-grips on rod, move to and fro with a good degree of resistance) but I'm not sure if this is everything re the turbo - are there any oiling points / things to check?

Also, could there be anything else? It's really only limited to extreme load (big long hill, 70+ mph)

Don't have access to a diagnostic, and there are no lights on the dash (for the moment, having just replaced the ACE pressure transducer!)

Thanks all in advance!

When was the oil changed in the autobox last time? ... it might be a torque converter shudder as well which can be the result of buildup of deposits due to old oil

@sierrafery, actually couldn't say with any confidence re the oil - but good call, thank you. May be worth doing a bit of a swap / freshen-up, it's only the cost of the oil....

Not just the oil, the filter too: http://www.discovery2.co.uk/Autobox_Oil.html

sierrafery said:

Not just the oil, the filter too

Click to expand...

Duly noted, thank you! Ignorant question, but would the TC shudder be evident if it was locked? As I say, it was that happy place where the TC was locked, and rolling along at around the speed limit with 2500ish rpm showing... I tried to avoid a throttle position that disengaged the lock on the TC, or kick-down.

It usually occurs after the TC lockup but even if it's not that as you dont know about the oil it's to be replaced anyway