Bad idle when hot

[BillW]

I know e28s, but not M5s.
A friend bought a M5 that needs a clutch.
the car starts okay, but runs bad when it warms up. any ideas?
Could be old gas he says. I fear a head gasket issue.

[Randomg]

Coolant temp sensor, intake leaks.

[BillW]

temp sensor would be a good solution.

[Philo]

check the 02 readout when warm. I can't remember the pin number on the diagnostic connector.. I dumped my AFM and diagnostic connector. But at warm idle the voltage should swing between 0-12 volts.... If the voltage hangs more towards 12v and makes short swings back to center (6v) your lean.., and this will make for a crappy idle. At this point I'd suspect an air leak. Do a search, there is a ton of info on this.

Also.., just for grins.., put in some fresh plugs.

[sher judge]

Have the idle-valve checked?

Check all your pipes, also your throttle body big in-take rubber pipes.

Can cause serious idle problems @ high temps.