I have an old Saab 3l tdi which runs perfectly on short trips, but after 20 miles or so the Car appears to lose any turbo boost. Engine still revs and is drivaable but it loses all kick from the turbo.

If I switch it off and restart an hour or so later the car works just fine. Any ideas?

No smoke coming from the car so I suspect its a sensor causing me the issue.

Wastegate sticking open?

would that cause an intermittent issue? only happens after about 20 miles of driving. Are the expensive. I’ve also heard the MAF may be screwed?

Stuck vanes if its a vnt turbo? Try some archoil turbo cleaner through the fuel

The turbo turning off is probably because it has detected too much boost pressure, and is turning it off to prevent it destroying itself, aka limp mode. Usually caused by sticky turbo vanes or sometimes a dodgy boost pressure sensor or wiring.

Vanes can be freed up with treatment. Mr Muscle works if you can get at them; there are squirt-in foamy chemicals that you can spray in there, comes as a two stage kit thingy; but the best is supposedly Forte turbo cleaner that is meant to be trade only but loads of it available on ebay. Use alongside forte injector cleaner. I think it suggests two bottles to a tank if you already have problems whereas one for prevention. Will make your car go really well when its in the tank, but returns to normal on the next fill. Hopefully with problem solved though.

Google sticky turbo vanes for your car.

It’s going into limp mode, the wastegate is sticking because you’re only doing short runs and the system isn’t getting anywhere near hot enough to burn off carbon deposits.
This used to happen with monotonous regularity on my Octavia, because I was driving to work, a journey I could walk in less than fifteen minutes! I’d get it cleaned up when I had the MOT done, but it would come back pretty quickly.
Now I don’t drive to work, I rarely have it happen, but there are odd occasions when I’ll accelerate hard and it’ll just go flat, so as soon as I get into stationary traffic I switch it off then turn back on again, which clears it.
Doesn’t hurt to give it an Italian tune-up and find a straight, empty bit of road and accelerate hard in second to burn the crap off, then do it again as soon as possible.

Count Zero…I just tried that! Took it out, found a quiet bit of road and floored it a few times. Good news the power was all ther…bad news was that the engine warning light , abs and traction control light all pinged up when I hit a certian speed.

Stopped, switched turned it off on and on the abs and tractin corntol lights went of but the engine management light remains. Turbo worked fine throughout so not going into limp home mode!

IfGiven I usually drive like a pensioner I’m not to worried if the car only does this when I drave at silly speeds, but I’m thinking my bargain Saab may not be the bargain I thought it was…sounds like bill could be expensive!

When my Bora used to do this I used to switch it off and switch it on again and power was restored, sometimes I did this at speed 😯

It eventually led to a dead Turbo, The intercooler was full of oil like 2-3 litres.
It might be worth popping the pipes off and emptying it. Bear in mind as soon as you pop the pipes off it will pour out.
Very easy job as the intercooler is most likely in the bumper area so get a washing up bowl ready.

You need to get the fault codes read.

but the engine management light remains.

They are programmed to stay on for a certain while, particularly with a fault like this which can be intermittent. You won’t have cured it completely, just freed it up somewhat. A lot of hard driving might, but you’re better off with a long steady high speed trip rather than lots of flooring it at lights because that produces the smoke and the gunge that causes the problem. Road trip to Germany.

The intercooler thing is not a bad shout either. I have a front low mounted intercooler which means that I could remove the undertray and pop the hose clips off and give it a bit of a clean. It’s fairly normal in older cars btw for oil to build up in there. I only had a few tablespoons though so it didn’t gush.