174 Turbo limp mode issue

Hi All, having a few issues with the old T5 174 AXE. Ive had it from new and had to do a couple of major jobs, turbo replace, ex manifold split, clutch and flywheel, driveshafts etc. I now have an issue that has been plaguing me for a while. It repeatedly goes into limp mode!! It used to do it very rarely. The first time was very embarrassing as I'd just passed an evo and was fair tramping up a hill on full boost. No warning just into limp mode. pulled over and left it for a bit thinking it had just been 'worked a little hard' . I started it up again and no problem at all. after that it seemed to happen occasionally normally under strong load situations. it always just drops to the 2 k revs and thats it. I don't use the van very often as i try and keep it mint. Anyway the problem now is the amount of times its doing it. i haven't used it for a couple of months and within 2 minutes on the motorway yesterday at mid revs it just went into limp. turn the key off and back on and she's good for another 1/2 mile. if I rev up and down up and down constantly it is alright it just when you stay steady.

Hi Grego, thanks for your input.

Well, in case the problem was directly related to lack of use I thought id cane it down the M4 1 junction. it turns out that I am correct in the assumption that if power it on and off it doesn't go into limp mode, if i just leave it on a 'turbo demand' at some point it will go to limp. so I can make it not happen and I can make it happen. Whilst I was going down the M4 at slightly above the national speed limit, but not fast enough to get sent straight to jail, with the on and off throttle process I blew a charged air pipe off! the horrible little pipe that exits the N/s of the intercooler and meets the plastic with the MAF sensor in it. as has happened to me on numerous occasions now the lugs had come off the male bit! plenty of black smoke and booming noise I managed to limp home and order another. Having removed old pipe and sworn and got moody about this sh1te design letting me down for a fourth time i looked into some other things.

Right 'suck checked' the vac pipe from the turbo. I can suck the actuator round with a lot of effort and put my tongue over the end and it stays 'sucked on'. When I let go it goes back freely with no obvious restrictions. Ive sucked the one next to it on the N75 and that holds a vacuum as well. the third one that just goes back to a little open paper filter wont hold any vac as I'd expect. The one from the EGR that is blanked by the way will suck back to the same paper filter. I cant find the one that goes to the EGR cooler or the rocker cover. This is one of the earlier 06 models without the electronic EGR. maybe it doesn't have those vac pipes.

Now its getting interesting, I have replaced pipe this morning and ended up with some weird noise that turned out to be a woofling on over run of the turbo, didn't have a clue what was causing that! i disconnected the actuator vac tube from the N75 and it stopped doing it! so replaced the N75 then and there!. it still wooffles a bit on the run down if you floor it when its static. I don't know why yet. It goes better and you can now feel the turbo being smoother and progressing properly instead of like a wild 2 stroke motocrosser. It hasn't gone into limp again but I haven't given it a proper dual carriageway caning yet. Too many dibble about in the daylight. The limps would have come by now, so it has definitely improved but yet to see whether it has completely eradicated it. I am now going to try and find the cause of the wooofling and report back. Thanks for now folks.