Over-revving and sticking in 4th & 5th...

Gentleman - please could you proffer suggestions as to what this problem is.

I have a '92 110 2.5tdi LHD with 190k km on clock.
A couple of times in the last few days whilst in either 4th or top, when I put the clutch down it goes into seriously high revving as if in neutral - very dangerous on these island's roads.
At first I thought that the accelerator pedal was stuck, I had to cajole the brakes and the clutch to rectify. I pulled over, lit a cigarette and it ticked over quite happily in neutral. I drove the last few clicks back to the house very carefully and it was fine, if a little delicate.
I checked the oil yesterday and the dipstick was textbook.
I have been rummaging around here on posts and this chap has had similar problems - but mine are different I think.
http://www.landyzone.co.uk/lz/f7/my-90-revs-high-wont-stop-now-wont-even-start-56014.html
- I could not turn the engine off last week either (returned key to zero position and could even take the key out of the chamber and the engine kept running) Stalled it in top very slowly to stop it.
LR Mecanico here on the island said it could be either the stop solenoid or the key chamber. But the above corresponding post by NIGGLES suggests that it may be something to do with oil?
Would greatly appreciate any help on this as it may well cost me my job.

The added cockpunch being that it passed its ITV (MOT) today!

Cheers,
Matt.

It sounds to me like the "running on its own oil problem", which could either be something relatively simple to sort for your self or a total engine overhaul.

Here's a link to a similar topic:
http://www.landyzone.co.uk/lz/f7/2-5-turbo-diesel-58218.html

Ofcourse with your engine having a turbo, it could be that one of the oil seals has started to give way (within the turbo unit) which is literally spewing oil down the air intake. There are ways to see if this is the problem. You need to remove the air intake pipe from the engine side of the turbo and check for oil residue. If there is some oily residue, the problem is more than likely being caused by a fault / wear in the turbo unit.

Also try running the engine with the breather disconnected or the filler cap off and check for pressure. You can't go wrong with the dipstick pressure test explained in the above link!

Let us know how you get on, what you find!
-Pos