Mk1 TT Boost Issues
Discussion
I've just been to look at a 225 TT as a runabout. Lovely car, felt solid, was in good condition, never modified, but during the test drive it felt more like 100bhp and that the boost came in and out sporadically. When you planted the throttle at, say 2-3k revs you could hear the turbo spin up as expected, but the boost would occasionally drop off at 4-5k revs and the car went totally flat. It certainly wasn't putting out 225bhp at any point. There were no untoward noises, it idled well, sounded smooth, didn't misfire, no smoke, etc.
I couldn't do a deal on a car with issues. Does anybody have an idea what could be wrong? It would be a shame to let an otherwise good car go for the sake of a simple fix. Unfortunately the lady owner didn't see the issue. I expect she has become used to the comparative lack of power and just drove to suit.
I couldn't do a deal on a car with issues. Does anybody have an idea what could be wrong? It would be a shame to let an otherwise good car go for the sake of a simple fix. Unfortunately the lady owner didn't see the issue. I expect she has become used to the comparative lack of power and just drove to suit.
I have had my 180 quattro since 2001. The engine / turbo feels as you say， & I found this more noticeable last 2-3 years. I highlighted exactly the same points each time I brought in my car for service & everytime I was told the turbo was behaving in perfect order， the readings normal etc.
I think what it is is that having driven more modern turbos in recent years made me forget the Mk 1 is an old car with old turbo technology. To be honest in 3rd or above the turbo is very minimal as far as i can tell， and its always been like this， unlike my other modern cars turbo （ mk 3 TT） can be present anywhere in the rev range given any gear. But i suspect this is why my mk 1 is more enjoyable to drive.
I am no mechanic hence I do not know if the car you tested has a fault，but your description fits in mine. My advise is old TTs can have many wear & tear issues. Mines been visiting the garage almost every other month for the past 2 years. This month cant get into 1st，& battery went dead， last month the roof cloth lining fell onto my head whilst driving， month before there were some cracked pipes leaking foul smell into the cabin. And sensors， they always manage to find a fault somewhere that requires replacing.
Better get professional help if you really liked it
I think what it is is that having driven more modern turbos in recent years made me forget the Mk 1 is an old car with old turbo technology. To be honest in 3rd or above the turbo is very minimal as far as i can tell， and its always been like this， unlike my other modern cars turbo （ mk 3 TT） can be present anywhere in the rev range given any gear. But i suspect this is why my mk 1 is more enjoyable to drive.
I am no mechanic hence I do not know if the car you tested has a fault，but your description fits in mine. My advise is old TTs can have many wear & tear issues. Mines been visiting the garage almost every other month for the past 2 years. This month cant get into 1st，& battery went dead， last month the roof cloth lining fell onto my head whilst driving， month before there were some cracked pipes leaking foul smell into the cabin. And sensors， they always manage to find a fault somewhere that requires replacing.
Better get professional help if you really liked it
I have had my 180 quattro since 2001. The engine / turbo feels as you say， & I found this more noticeable last 2-3 years. I highlighted exactly the same points each time I brought in my car for service & everytime I was told the turbo was behaving in perfect order， the readings normal etc.
I think what it is is that having driven more modern turbos in recent years made me forget the Mk 1 is an old car with old turbo technology. To be honest in 3rd or above the turbo is very minimal as far as i can tell， and its always been like this， unlike my other modern cars turbo （ mk 3 TT） can be present anywhere in the rev range given any gear. But i suspect this is why my mk 1 is more enjoyable to drive.
I am no mechanic hence I do not know if the car you tested has a fault，but your description fits in mine. My advise is old TTs can have many wear & tear issues. Mines been visiting the garage almost every other month for the past 2 years. This month cant get into 1st，& battery went dead， last month the roof cloth lining fell onto my head whilst driving， month before there were some cracked pipes leaking foul smell into the cabin. And sensors， they always manage to find a fault somewhere that requires replacing.
Better get professional help if you really liked it
I think what it is is that having driven more modern turbos in recent years made me forget the Mk 1 is an old car with old turbo technology. To be honest in 3rd or above the turbo is very minimal as far as i can tell， and its always been like this， unlike my other modern cars turbo （ mk 3 TT） can be present anywhere in the rev range given any gear. But i suspect this is why my mk 1 is more enjoyable to drive.
I am no mechanic hence I do not know if the car you tested has a fault，but your description fits in mine. My advise is old TTs can have many wear & tear issues. Mines been visiting the garage almost every other month for the past 2 years. This month cant get into 1st，& battery went dead， last month the roof cloth lining fell onto my head whilst driving， month before there were some cracked pipes leaking foul smell into the cabin. And sensors， they always manage to find a fault somewhere that requires replacing.
Better get professional help if you really liked it
Cheers guys. It does sound like the N75 valve for controlling the wastegate, but I'm not buying one for a car I don't own and couldn't get a deal on. The more I've thought about it today the more I'm put off. The car was otherwise immaculate and I can believe the owner doesn't see the issue, but it was definitely well down on power. To the guy with the 180, it might be worth trying the N75 valve on yours.
Also sounds to me like the diverter valve. A very common failure.
Ask the owner to get it changed (and/or N75 for peace of mind).
The other common running fault on 1.8Ts is the airflow sensor (MAF) although your symptoms are more conducive to the diverter leaking boost under higher pressures.
Ask the owner to get it changed (and/or N75 for peace of mind).
The other common running fault on 1.8Ts is the airflow sensor (MAF) although your symptoms are more conducive to the diverter leaking boost under higher pressures.
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