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So the saga of the m5 continues . Replaced Ignition coil , leads , dizzy cap, rotor button , all senors intake etc and coolant sensor, Vacuum for intake flap , Full service , Injectors <New>,Radiator fan and clutch .Cleaned maf . If unplugged runs even worse . Car still hunts. @ idle .Idles @ 700 , then 800 but never really even . If I rev it up it drops to a almost stall then returns to a uneven idle . I have noticed that it idles much better with the lights on .I thought id check voltage from battery < New Battery > , I was getting 9volts @idle , Lights on 9 volts . If I rev it up.... 9 volts. Battery however remains charged and cranks over very fast and no low voltage lights on dash . My thinking is that if it was charging properly @ say 13.5 the idle might even ?? . Any ideas Most welcome .Thanks In advance :1zhelp:
 

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Hi, is that 9 volts measured at the battery? If so what is the voltage at the positive point in the engine bay? If that's >13 volts with the engine running then there must be a bad connection somewhere. Try checking the earth strap from the battery to the chassis. Of the list you just put up you haven't mentioned the idle control valve, has this been checked?
 

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I had similar symptoms that was cured by a combination of new alternator, voltage regulator, battery cable. Just replacing the alternator and voltage regulator helped the issue, and it was further improved by replacing the battery cable.

However, in my case, turning on the lights made the situation worse, not better.
 
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