VW Bora 1.9tdi ASZ limp mode, please help.

[CRFSAM]

As the title states I'm having issues with my VW Bora going into limp mode. I have read various posts about the same issue and was hoping I would resolve the issue before creating another duplicated post, but I have not. I have a 2002 Bora, 1.9tdi, asz engine code, 114k. I have only had the car 2 or so months and travel 200 miles each way to work once a week. The car goes into limp mode after around 50 or so miles when just driving at 80mph or so, stop turn the car off back on again same thing happens so reset again and then is fine. It's only ever done it a maximum of twice in the 200 mile journey, I am not hammering the car just driving steady and achieving 57mpg. On a few occasions I have done the journey and nothing has happened and I thought it had sorted itself out. I have had it read twice and got the code 1557 which I'm aware is overboost positive deviation. With this fault not always happening and not happening under hard acceleration would I be correct to assume it may not be the turbo? I was going to do the N75 valve and then go down the turbo route? I've had turbo cleaner in the fuel tank and it's obviously done nothing. I've also noticed a build up of oil on egr which I assume is coming up from the intercooler, would this cause the issue? Any help would be greatly appreciated, I do not have access to vagcom etc.

Sam.

[zollaf]

its almost certainly the vnt mechanism within the turbo sticking. most other things, the n75, worn hose etc cause negative deviation. try giving it a good italian test tune , trying to get 27 mpg instead of 57, that might work, foot to the floor holding the gears until almost the red line, actually get the turbo working. i did this to 1 a couple of years ago and its actually been fine since. gig cloud of black smoke came out the exhaust, poor thing was properly choked up.

[CRFSAM]

Thanks for the reply mate, maybe I'll get some v-power in her and give it a good drive then. I'm prepared to have the turbo replaced I just want to be sure it is and it not end up being something cheap and stupid.

Cheers.