I have 2001 Passat 1.8T with APC engine, runs perfectly except for when in traffic on a hot day 40c engine starts to run rough, clears if I shift to neutral and rev for a while at 2000 or so RPM
I ended up taking my Passat to someone that could check the diagnostics out on the computer, found that one breather pipe had aged and cracked longitudinally and one of the vacuum hoses rubber had softened with age and was pinching closed when the engine was running hot. Both hoses replaced and car running perfectly!
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