Idle fluctuation and long crank issue only when slight warm
 

So it goes like this, and the car is a 530d Automatic 2005:

1. When the car is dead cold, even at -16 C, starts perfectly, idle is steady, crank is super short, basically, everything works perfect.
2. Now, after I drive like 7km, so the engine gets barely warmed up, all the troubles start, as follows:
- idle fluctuates, up and down, not dramatic, but still very noticeable, also, this fluctuation it is noticeable if I put the car on cruise control, barely, but it's there.
- if I turn off the car while in this state of engine not being fully warmed, it will take like 15-20 cranks to start, this does not happened when the engine is either stone cold, or when it's at operating temperature. So it turns very quick, but takes a lot of spins till it starts.
So the two problems seem to be correlated (fluctuating rpm idle and this super long cranks), and present only when the engine is slightly warmed, everything goes away after it is fully warmed.
3. After I drive some more and the engine reaches full operating temp, ALL OF THE ABOVE goes away, idle is perfect, crank is perfect.

I have absolutely no error on every tester they put on my car, no codes no nothing.

The only thing I know I need to change is the big thermostat (it sits at 75C while driving, only goes up to 91C when stationary so it's stuck open)

The car was fully serviced a month ago, filters, oil, fluids, crankcase breather, egr thermostat , some vacuum control valves, egr was cleaned also the intake etc., battery is new, glow plugs new and I only use premium fuel, along with some fuel additives every so often. Live data shows that the injectors are working fine and in range.

Could anyone point me into some direction?

I am thinking to replace both Crankcase and Camshaft sensors, though they don't throw any errors.

So basically all of my problems are present only when the engine is warmed just a bit, never when it's fully hot and never when it's cold.

Changing these sensors is the best course. Next would be MAF sensor (if you have one).

so it turned out to be the goddam voltage regulator, unbelievable... I got the problem backwards, the voltage does not drop because the idle drops, but the other way around, the idle fluctuates because of the voltage drop i.e. because the alternator stops working, interrupts, because of the bad voltage regulator.

changed the regulator, back to normal. jesus.

That was unusual because there should have been an error code regarding generator/voltage regulator. I had the same problem (idle rising/falling) before but WITH a generator error code. Good you found it.

Wow, I certainly wouldn't have guessed or looked for that.

yeah well I got lucky, because I had a sudden "charging fault error", and the mechanic had this evrika moment.

still, now I get some weird battery drain issue along with the famous "high rate batt discharge", though there is no parasitic draw (tested with the multimeter, I get only 0.01mA after shut down).

damn car is killing me.

There is a very specific procedure to test a BMW E60 battery drain (newtis). Your IBS is most probably the problem. Unplug it or change it.

Would you be so kind as to point me towards this drain test procedure and also how do I disconnect the IBS? As I said, I unplugged the small blue connector, but I fear it's not enough.

Thanks!

Their are videos on YouTube that shows you the removal of the IBS

I would and tried 20 minutes, but I can't find it atm :hmm:.

Here: https://www.newtis.info is EVERYTHING for your BMW, every wiring diagram, every repair manual. I do know for sure the procedure is there also, because I checked it a few weeks ago (and found it easily) but I'm lost today.

Edit: Here: https://www.newtis.info/tisv2/a/en/e60-525i-lim/wiring-functional-info/body/voltage-supply/energy-diagnosis/

Look for your car of course.