E39 528i flat spot

All,
My 528 auto has an annoying flat spot around 2500 - 3000 rpm ... it doesn't have it all the time but seems worse when it's hot - she's certainly
fastest when the engine is cold (unfortunately).
Is my 'vanos' unit, or perhaps the control solenoid kapput? (I have the single vanos unit it seems)
tia
Steve
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have you checked the ground? I've seen bad ground at the ignition coils do similar problems. for some reason bmw's and mercedes have lots of electrical problems for at least the past 8 years.
Oskar
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