MK5 Golf GTI
All Things Mk5 => Mk5 General Area => Topic started by: MF_TSI_170 on September 10, 2025, 11:31:50 am
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Hello people,
I have a tsi 170 twincharged not a gti , 2007 gt. I’ve only had the car a couple months but I’ve been having some boost issues. Some general information about the car- 85k,2007, very well maintained previously, full service & stock.
The first issue started about a week after buying on 79k where the turbo wouldn’t spool at all after the supercharger phase so would provide a nice jolt when the supercharger cuts out and the turbo didn’t kick in. I replaced the n75 after a bit of research and that seemed to sort it for a while.
Now my current issue is when under a higher boost load I’m getting a lot of fluctuations in pressure, my model has the stock boost gauge and you can see it repeatedly dropping from 100% to roughly 75% and back up over and over quite rapidly. This mainly happens during the turbo phase but has happened a couple times during the supercharger phase. Another thing is during the turbo phase you can hear the watergate opening and closing rapidly(not metal the air) as the issue happens and sounds like it’s not closing fully.
Originally I was thinking wastegate gone bad and isn’t closing properly, but since it happened once or twice in the supercharger phase I’m now thinking dv or map. Any suggestions of what it could be before I book it in to get diagnosed?
Had a recent service but this issue was happening before that anyway, no boost leak and no noises that would suggest either has failed.works flawless and has normal power if you just hold it at 75% boost and not floor it.
Regards,
Ethan
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I would be plugging into VCDS to see exactly what errors/issues have been logged.
The N75 on the GTI controls the boost and they can become faulty
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Before I had the n75 changed it had P0299 low boost. But now that’s replaced the turbo has no problem building boost it just won’t sustain it for more than a second without the wastegate opening.