I'm hoping this is just a case of the map sensor being on the blink (as I have a spare 2.5 bar sensor anyway)

Is this kind of fault code likely to be anything else serious? I think I had it when one the vacuum pipes on the mongrel had a hole in it. Worth checking those too I suppose.

It means your not making boost.

N75 or a vac pipe off like you say. Or a stuck turbo, although that usually results in overboost.

hoping it isn't the turbo as I had good full power yesterday after changing the MAF. It just seems to have developed overnight.

Ive had this code too, which was a stuck turbo.. only did it when cold and on moderate throttle

Well, this morning I had boost again, and on the way home - until I booted it at 40mph in 3rd. Threw into limp mode at about 3500rpm, and it's amazing the difference when it does it.

So, how does one clean out a stuck turbo? I'm not surprised it is sticking though as the previous owner must have ran the car in limp mode for a couple of years or so.

You have to remove it and strip it down into pieces usually.

There was some magic foamy stuff I saw advertised a while back that was supposed to work pretty well. You take off the downpipe and squirt it in, it breaks down the carbon.

This link should give you some idea of what's involved....

Turbo Clean

HTH

Can I do a "fingers crossed" trick and hope it cleans itself out gradually now it has boost back and is being moved about a lot more regularly? I have not checked the N75/vacuum pipes yet, so it may well be something less serious.

It wont clean itself out.

It wont clean itself out.

bugger Oh well, time to get my hands dirty again I expect.

Thanks for the above link Td-eye

When I stripped and cleaned the turbo on the Passat, the hardest bit was removing it from the car.

When I stripped and cleaned the turbo on the Passat, the hardest bit was removing it from the car.

Did you get a similar fault code? What gunk did you use to clean it? I would imagine brake & clutch cleaner is about as tough as you'd want to start using on the turbo internals?

I've just had a thought - If there was a dodgy clip or something somewhere between the turbo and inlet, this would also cause the negative deviation code, yeah? I.e the car is requesting full boost, but only getting 3/4 boost due to 1/4 hissing out some dodgy joint?

As I said earlier a leak usually causes an overboost fault as for a moment the turbo tries to compress atmostphere and the boost spikes upwards and goes into limp. But it could be a leak. these are all things to check first before jumping in with both feet.

When I stripped and cleaned the turbo on the Passat, the hardest bit was removing it from the car.

Lest not forget the passat being somewhat easier to work on being longitudinal...

I couldn't get the car to go into limp mode this morning, despite me putting quite some effort into making it do it.... Bloody skodas.