M5 LOSING POWER

On cold start ups the engines starts to buck and when engine warm cannot go past 5000 rpm and check light goes on . Checked for faults ( all cylinders
misfire ) need to find an answer . HELP
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of M5s - E28, E34, E39 and E60?
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It sounds like 02 sensor problem that could be related to an intake manifold leak. Other related problem I saw was oil that leak in spark plug hole.(leak cause by bad cyl. head cover gasket) That kind of leak can kill ignition coils as well so check it out. So I'll check first---oil in spark plug recess and change inner and outer head cover gaskets if required and don't forget the round rubber seal for the fasteners, they dry out pretty fast. You did not specified mileage/km but may be it's time for new plugs anyway... 2---intake leak -- check all rubber line/crankcase ventilation and oil separator component. Ensure all throttle bodys are all thight (torque to 15Nm /11 lb/ft) After being sure that both air and/or oil leak are fix and/or fine I'll go for the 2 rearmost O2 sensor (the monitors) then the forward ones if problem persist. 3--- lately your problem could be related to an internaly destroyed/or clogged catalytic converter(s). That means $$$$ if out of warranty (6 years) Note: Make sure to disconnect the batery first and then the ECU for at least 10 minutes before running eng. (after fixing any of those things). That will reset the ECU back to is normal operating setting. Internal adjustement is done to the air mixture due to small air leak and normal wear component, but there's a limit and you are already out of this limit. The other way is to let the eng. idle for 30 minutes but it's a waste. So..disconnect...fix (any of those checks and fix will take more then 10minutes)...reconnect... run (and hopefully enjoy). In my case (M62 eng.) things get better after changing head covers gaskets and re-torque the intake, but still had misfire occasionaly (1-2 times a month) but after replacing the O2 sensors monitors everything went back to normal...for 6 months til I changed the 2 others O2 sensors since then (40,000 km) everything's fine and I'm running 305,000km. But a friend of mine had to go all the way to the cats replacement.
Good luck

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