UrS4 low boost problem ... SOLVED!
After nearly 3 months of owning my S4, I've finally cured the low-boost problem it's had since I acquired it by fitting a new wastegate frequency valve (WGFV)! (For reference, the AAN uses part number 034 906 283 H - I got mine from the very helpful vagparts.com for a good discount over the dealer price.)
The symptoms I experienced were that from a cold start, the car would produce decent boost maybe once or twice, and then peg boost back to a purely wastegate controlled 1.4 bar. An ECU output test would happily cycle the WGFV, so it's quite obvious that the valve can still appear to work while not being able to control boost properly ...!
It's been a really useful learning experience, and I now feel I've got a good understanding of "how things work" with the boost control system. For good measure I've also now fitted a new 710N (Audi S3) diverter valve.
To say I'm blown away by the restored performance of the car is an understatement! Now I finally understand what all the S-Car fuss is about
And to think it is costing me LESS to insure than my old Mk2 Golf GTI ...!
Cheers for all the advice and info I've gained from the forum. Wouldn't have known where to start without you!
Andrew
The symptoms I experienced were that from a cold start, the car would produce decent boost maybe once or twice, and then peg boost back to a purely wastegate controlled 1.4 bar. An ECU output test would happily cycle the WGFV, so it's quite obvious that the valve can still appear to work while not being able to control boost properly ...!
It's been a really useful learning experience, and I now feel I've got a good understanding of "how things work" with the boost control system. For good measure I've also now fitted a new 710N (Audi S3) diverter valve.
To say I'm blown away by the restored performance of the car is an understatement! Now I finally understand what all the S-Car fuss is about
And to think it is costing me LESS to insure than my old Mk2 Golf GTI ...!Cheers for all the advice and info I've gained from the forum. Wouldn't have known where to start without you!
Andrew
...Waste Gate Frequency Valve to replace first! 
I think I was just a bit thrown by the fact that it "seemed" to be operating okay during the output test, and the additional fact that everyone seemed to be pointing towards a boost leak.
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