Our AAN engines are controlled by a computer (ECU or "ECM"). This ECU controls boost pressure by either holding or dumping boost via a waste gate frequency valve, N75, aka "pulsed charge pressure control (CPC) valve". The N75 is located near the front of the engine, near the MAF to turbo hose, as shown here:
This is what VAG says about the N75:
Also from the VAG Self Study guide 111
Pertinent N75 PN's are:
034 906 283 J = stock 3B (in 200 20v and S2)
034 906 283 H = stock AAN (UrS4 and UrS6)
034 906 283 K = S2 ABY and RS2 ADU
Link to European Car N75 article on Skollie's server
Here are some N75 function explanations from Paul Nugent at S2Central.net:
and
Scott Mockry at his SJM Autotechnik website outlines an N75 test procedure that might be of use.
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