E46 M3 wont rev past 4000rpm

Calling all experts!!!

I am thinking of buying an E46 M3, car is in fantastic condition, with one major problem, it wont rev past 4000rpm (thankfully I took it on a longer test drive today) gets to 4000rpm and its like a limiter kicks in, it coughs and splutters and gets maybe to about 4500rpm (which is as "hard" as I would push her.) Basically feels like she is in limp mode.

MAF Sensor? software issue?

Any ideas Gents ?

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looks like it is MAF sensor, according to:

http://www.m3forum.net/m3forum/showthread.php?t=25228