Mk5 Gti cold boost issues and sloppy gear changes

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PUNK
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Mk5 Gti cold boost issues and sloppy gear changes

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Hi all,

I’ve got a very weird issue lately I haven’t been able to diagnose.

On cold startup and driving it feels like the turbo is overworking but not providing smooth boost or power delivery almost like something is blocked. The turbo and exhaust also make a louder noise than it should. This happens intermittently up until I get to about 3rd gear (DSG), automatic gear changes are also very ropey during this time but then from about 30km/h it feels like the blockage is released and turbo and gearbox changes are quiet and smooth again and power comes back. Almost like a valve has been opened and boost floods back in.

I’ve replaced the following over the past 6 months:
Plugs, coils, sparks, cleaned injectors and carbon clean, n80 fuel breather, carbon canister, pcv kit, full service etc.

I’ve just had the car in to have the turbo inspected as it developed an oil leak. They gave it a kit overhaul, no cracks in the manifold and replaced the gasket to downpipe but still the same boost issue after reinstall. Turbo guy is stumped and very kindly offered to try replace my refurbed turbo with a refurbed unit he had on the shelf to test but doesn’t foresee that to fix the problem.

Any advice on where to troubleshoot? I’vw read a bit about the n75 valve (which I haven’t replaced) issue which hasn’t been conclusive.

Also no engine codes on VCDS

Thanks
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