Sorry for the delay - been a bit busy - but here is what I have done which seems to have fixed the problem. May help someone in the future. Referring to my earlier post having thought that maybe part of the problem is the TPS I removed it completely from the throttle body. Took a bit of gentle persuasion as there was a fair amount of corrosion in the throttle body fitting. (been there for 110K miles all weathers)
Checked the resistance with an accurate DVM to see if the output was smooth over its range and all seemed OK. Unfortunately the Data sheet for the 4 contact TPS does not give absolute resistance values, only ratios. However the resistances increased consistently without any jumps so I figured it was probably working OK. So having cleared out the corrosion I refitted the TPS and carried out the “Zero = Zero” process.
Now here is the rub. The left hand cable from the combiner unit is too short. (I bought a new one in case mine was a rogue but the new one is exactly the same) To get the throttle onto its stop the adjuster is slackened off fully and I mean fully. Therefore to slacken off the throttle stop screw to fully close the butterfly I had to disconnect the cable. Any way I unscrewed the stop screw until there was a gap and the butterfly fully shut. (during the overhaul I had thoroughly cleaned out the throttle bodies and polished the throats – there was quite a build up of ingested oil via the air box breather – do you remember to drain the air box occasionally via the drain plug at the rear nearside corner? – I was surprised how much oil had collected there.)
Connected wires to the TPS as the various methods say and set the TPS to its minimum voltage with the ignition on. Lowest reading was 2mA so to make sure I was on the end of the pot I set it to 3mA. Lock the TPS there and then adjusted the throttle stop screw to give 360mA. Locking the screw with everything in place is a bit of a fiddle so once locked down the reading was 376mA but OK in the stated range of 360 to 400mA.
Reconnected the cable and fortunately could still get the throttle on the stop! Set the 2 idle screws to one full turn out connected up the TwinMax. Pulled fuse 5 for a minute to clear the Motronic then with the fuse in and ignition on gave the throttle fully open a couple of times started the engine – no problem. Then when warmed up set the RH throttle stop screw to balance the throttles. Then adjusted the cables to balance the throttles through their range.
Idle speed did not need adjusting from the initial setting of the idle screws – one full turn out.
Did a test ride (60ish miles) and the bike is better than ever. It was never very happy at lowish revs in 6th but now I can happily tootle at 30 in 6th and it will even with gentle throttle accelerate away in 6th from 30.
Conclusion:- the initial problem was probably a failure of the Lambda sensor but at some time when I was using BMW to service it some one readjusted the TPS. Obviously the Motronic could cope with the TPS being slightly out but once the Lambda went it all got too much. Plus the slight build up of crud in the throttle chokes over the miles probably did not help. But now I have an 11 year old 110K miles R1150GS which is running like new!
Thank you all for your comments I hope this helps someone else in the future.
a couple of times but no noticeable change but when I got home the old idle problem was back. I need to do a bit more investigation myself but any thoughts out there?
