Possible boost leak?


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Apr 17, 2010
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I've done a bit of hunting around and others have reported similar problems to mine, but nothing seems to match exactly. Iv'e been having problems for a while, so I'll try to be as specific as possible with what I've done so far.

Firstly the car started having terrible trouble with power loss. It would run lumpy at idle and properly struggle to get up the 1 in 4 hill I live on. Stopping, switching the ignition off and on again would get me up the hill, but still low on power. I had the MAF changed, didn't sort it. A throttle body clean eventually fixed the power loss, but not the lumpy idle. In an effort to get the idle fixed, my mechanic changed my divert valve with his, used but known working, part. Doesn't seem to have fixed the issue.

Since the divert valve was fitted, I've noticed a dump valve sound when lifting off the accelerator. Doesn't bother me all that much (it's even quite fun on occasion as chavs in their Saxos go visibly green when it happens right next to them), but I'm wondering if it's related to the main problem I have.

The big one is that the turbo seems to be sporadic. It is most noticeable when the engine's on full chat, particularly in second and third gears. It comes off and on as if I'm pumping the throttle. I can't hear any louder hissing noises than the usual turbo sounds and I'm not sure what I should be looking at. I know some people have experienced problems with the sensor on their airbox (N75?), but mine's a facelift car and doesn't appear to have one. I've also heard that the breather pipes are prone to crack and split, but people with this problem seem to report a more constant loss of power than my off-and-on issue.

It's a 2001 1.8T and I hope somebody can help point me in the right direction. I'm not a car novice, but this is the first turbo I've had and I'm at square one with it.
I feel your pain mate - I think I have something very similar.

I took my car in for a remap last week and had a forge DV and pipercross panel filter fitted at the same time. The noise from the turbo spooling up is now louder (I guess because of the filter), and the dumping sound that the DV produces is awesome....BUT...

I'm convinced that I'm not running at full power. I had previously had a Revo 5 hour trial and the guy who mapped my car told me that the trial is about 80% of the power that I'd get from the full thing, but if anything, the trial seemed more powerful! The thing that is concerning me the most is the turbo noise - it seems to spool up nicely until about 3.5k, where it completely STOPS making the spooling noise. If I stay on the accelerator, the noise seems to start coming again at about 4.2k...but it's very faint. Does this sound like boost leak? I also have slightly lumpy idle, with the needle slowly hunting around. Is this related?

I'm going to persevere with it for a little while longer, then ring the guy who mapped my car if there is no improvement.

Sorry to hijack the thread, but I feel that we could have the same problem. Any advice would be greatly appreciated.
Any advice on this guys? Is it normal for the spooling noise to disappear?!
Well, I don't know how normal it is for split pipes to magically re-seal themselves (I'm thinking not very) but if that isn't what's happened, then it must be due to my switching to Shell petrol from Sainsbury's a few weeks ago as that's literally the only thing that's changed. The hunting issue still remains but other than that, all power's back. No hesitation, no problems at all.

@S3 Dave: If the pipe to the actuator had let go completely, is this what you'd expect to see?

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