Update to R12S idle on 1 to 1.5 cylinders
 

To those of you who haven't gone with RB-3 and are still having the symtoms I had. This is what finally fixed the problem. I changed coils, spark plugs, did extensive testing with GT-1 on all systems and still had the problem. Oh, I almost forgot the BMW fuel system treatment at 3K. No faults on the idle stepper motors. GT-1 said they worked fine. I took the left side off for visual inspection and noticed score lines on the plunger. Maybe this causes it to hang up occasionally. I installed 2 new ones and haven't had any problems with idle on 1 to 1.5. The R12S is the only model which uses VDO steppers. They are also made in Mexico. They are much larger than RT, GS, etc.
The R12S idle is not as smooth as the other models. Cams etc. At least mine idles on 2 cylinders now. Maybe this summer I'll go with RB-3.
regards, tjs

A potentially interesting post, tjs, except in my ignorance I don't know what you're saying. "I took the left side off for visual inspection and noticed score lines on the plunger." Are you referring to the throttle body? I've never looked in there....just would like to know what you are telling us at this time. My bike idles fine, but I'm interested in what was wrong with yours.
Thanks.

Is there any chance you could post pictures with the explanation, I'd love to see them. How do you have access to a GT-1? I'm jealous.

Bob. Idle control and cold start mechanism. System: The BMS-K controls the automatic idle system, as well as the cold start programming. The automatic idle is controlled by regulating the amount of air that it delivers in to the engine by a plunger type stepper motor, which are mounted on the top of both throttle bodies. The idle control motor,(stepper motor), is able to
regulate a large difference in air mass depending if it is a cold engine or at operating temperature.
If you to a search. R12S idling on 1 to 1.5. or R12S rough idle . there are post that explained the problem. I don't think the R12S will ever idle as nice as an RT.because of the way 12 more hp. was gained. tjs

JonM. The stepper motors are very visible. Just look at the top of either throttle body. It sits directly in front of the fuel injector nozzle. To answer the other. When I was on the computer earlier It was at work and GT-1 was directly behind me... . tjs

My bike was in for its 10 000 km service today and dropped on to 1 1/2 cylinders whilst the tech was doing the post service check ride , hooked it up to the diagnostics and gave it a good look over .

The tech was able to confirm the left hand idle actuator (stepper motor) was not moving whilst the right hand was , he cleaned it up (there was some carbon or other crap in it) and told me on the spot that if it does it again they will replace the motor . He said he had recently changed one on another 1200 (not a 1200S) which had the same problem .


Thank goodness it did it when it was in the shop.

The tech also told me that my Black Bike pulled significantly harder and was quicker than the Candy Cane bike that they have in the showroom SmileWavy