535 runs lumpy when hot

[E34my535]

Hope you can help - recently the alternator belt on my 1988 E34 535 snapped and since fitting a new one I'm having problems when the engine reaches normal running temperature.

Once the temperature gauge starts to read near the middle it starts running lumpily and in the end stalls. Its worst when it is at idle speeds and once it stalls it doesnt like restarting while still warm either - any clues??

Would be surprised if the alternater belt change itself has caused the problem but could the jump starting have caused some trouble?

[e34bim]

is the alternator giving out enough power like 14.5 volts when running "might be worn and the reason the belt snapped in the first place", it could also be the battery failing to hold a good charge

[bahnstormer]

battery is out of the equation when the car is running....

[E34my535]

Cheers for the suggestion

After the belt snapped I did get the alternator reconditioned and when it stalled after fitting the new belt and alternator I called out the AA and they tested the power at the battery. Reading was about 13 or so if I remember rightly - which he said was OK.

Also the dashboard battery light doesnt come on when its running lumpily so I had thought that this meant that the alternator is functioning as it should

[e34bim]

so alt and battery ok, next is idle control valve/rotary idle valve (clean it out) resistance between terminals should be aprox 40 ohms on terminal 1&3 and 20 ohms on terminals 2&3-2&1.
check for air leaks on vacuum pipes and clean the maf sensor

[DueyT]

Potentially in line with other recent threads on M30 valves, when was the last time you adjusted the valve lash. My motorcycle ran very lumpy in the last days of its stretched valves, before I had to replace the valves. The shims (moto eqvt. of adjusting rocker arms) were already at their thinnest accept. but when the engine warmed up and the valve stem expanded, the valves were no fully seating.

Just a thought...