I've noticed that when idling my 03 MC, every 30 seconds without fail the idle will drop about 200rpm, and then climb right back up. It does this all the time. Normal or not?

 

Mine does it too.... i think they all do it.
My understanding is that it's got to do with the fuel vapors being purged from the fuel tank back into the intake system.

 

Mine does it as well. I have not timed it but 30 seconds sound right.

 

My 2002 r50 has the same idle stumble. My mileage is also not the best. I plugged it into a scanner at a bmw aftermarket shop and came up with no codes. .
The dealer says He can check to see it the fuel injection software needs an updated for $130 to start with no promises . Sounds like a sucker bet. It amazes me this info isnt in their computers checkable from vin #.
this should work like online software with patches included in the original price. Dream on. Anyone else have this? experience. Im looking for input to help make up my mind. of course several people have said,. They all do that.

 

The scenario described above occurs when the radiator fan turns on!

Why?.............you have lost the low speed on the radiator fan.

Low speed should engage when the Engine Coolant Temperature reports a value of 105 degrees C.

Since low speed does not come on the ECT reaches 112 degrees C and the fan kick on at high speed.

High speed requires a lot more current; therefore all of a sudden the alternator becomes very difficult to turn and the engine stumbles! then recovers...........


The fan turns off when the temperature drops by 4 degrees C.

This cycle repeats itself over and over.


To verify if this diagnosis is correct, open the hood...the fan will start to run every time the RPM drops then starts to recover.


A decrease in A/C cooling will also be noticed!

Another way to verify with an OBD-II scan tool: monitor the ECT parameter; the fan Will run when the ECT reaches 112c.

Resolution: replace the fan (the low speed high wattage resistor located on the fan shroud is likely open)

 

You are correct sir. The stumble happens every time the fan kicks on.
My Haynes manuel lists a replaceable resistor but says you have to pull the radiator to replace it. Has anyone done this job? any short cuts or tips? Do you know the value of this resistor or can it be checked by wires without pulling the radiator?

 

Thanks for the feedback! I do not have a value for the resistor, but I seem to recall it was visible with the fan shroud removed, it may also be visible with the shroud in place. It resembles a large reel that is used for sewing thread except wire is wrapped around it.

 

Finally fixed my fan. The resister was shot. Almost $200 to replace a resister/relay. Im keeping my old fan and still searching for replacement resister/relay for the next time as this seams to be a recurring problem.I think its poor heat management to locate those parts where they are.
I am happy now because my mini idles smooth now. Quite a few people told me "they all do that". They were wrong.
Thank you for the help.

 

I've had this same problem but I also get a p2097 post cat fuel trim system too rich code with it. A BMW mechanic told me it's an intake or vaccuum leak but it does seem to only happen when the fan comes on. How can I test that resistor & where did you get one from? Any input is welcome of course.

 

I could not buy the resistor I had to buy the whole fan assembly. I bought it here. http://www.autopartswarehouse.com/sk...%26+Drivetrain
I dont know how to test this part with out removing the fan from the car, My resister crumbled when I removed the cover. If your idle dips 200 rpm then recovers when ever the fan comes on its not a vacuum leak. A vacuum leak would not be in sink with the fan.

 

Thanks for your insight, I'm going to look into it & see if that's my problem.