M42B18 won't rev higher than 3500rpm

[Suru]

Hello, my friend has a problem with his bimmer. He had bought it a couple months ago and everything was fine, now he can't rev higher than 3500rpm when the engine is warm/hot, when it's cold it runs perfectly normal. He has cleaned the flowmeter but it doesn't help. We can't do the stomp test because his check engine control doesn't work (damaged or removed). Previous owner chipped the engine and now the revlimiter is 7000rpm instead of 6500 (if it matter).

Cheers.

Mathew.