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There are lots of good 1.8T boost leak testing videos on YouTube and you can make your own tester with old tin cans or pvc pipe parts, plus a shrader valve.

In my low or boost hesitating problems, I’ve struggled with; i found my 710N diverter valve to be sticking from being warped by heat and n75 valve to be bad. Replacement of those boost control related parts; restored boost response and hesitation, sluggish boost response was eliminated, replaced by smooth boosting, much better throttle, power response.

I struggled for years, trying to figure out why my boost, was plagued with a hesitation issue, slow acceleration and overall sluggish performance. At that time, i found these parts to be in a “soft failure” mode; working, functional but not at the levels they should be, to deliver normal good engine performance, boost response.

Lately, i have been refreshing a number of aspects of my 1.8T, many parts being original, over 20 yeats old, to get it in top running condition; through investigation, found many old defective parts: hoses, pcv system parts, check valves, vacuum jet pump, hockey puck valve, etc., gaskets and things like injector cups (upgraded to aluminum billet; from plastic, which crack), seals, etc.

As each area, engine sub-system was gone through; parts replaced, updated and improved, my boost seems better and my fuel trims seem to improve, creating better overall drivability quality, performance.

Keep in mind, many aspects of the engine; all contribute, to create, good or bad drivability condition. I’ve learned allot during this process of: 1.8T, diagnosis, testing, refreshing and repair of old defective parts. After 20 years, many 1.8T’s are running poorly and there are many old parts snd problems; are contributing to this poor running condition. The good thing is, if you are dedicated to fixing things; you can restore the performance and fix the many typical issues that plague these 1.8T’s! These are great little engines, make a New Beetle fun to drive; when tuned up and running correctly! :)
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