V8 quattro 89

Does anybody have a glue what is wrong with a Audi V8 quattro 89 3.6L V8 which runs fine untill it reaches 1500rpm just like the ecu would be in
somekind of emergency mode ?
Is there a way to connect vag-com to that car and read fault codes and measurements ? I got a 303.1 version of vag-com available.
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