I'm going to try and avoid writing a novel here. As some may know my bike has a programmable SCS-Delta 400 ECU installed in place of the factory SC unit (it's made by the same company, requires no modification to the loom, it simply plugs straight in). The bike was returned to me a few weeks ago after being mapped on a dyno. The tuner wasn't happy with the idle - but tuner time is expensive time, so I figured how hard can it be.... Anyway after much digging, replacing of bits, multi-metering and trying to decipher the techno babble language that's the instructions for the ECU - I have made some progress I think worth sharing. First a picture... This is my bike currently! The big discovery I've made goes like this. Most of us who have checked our plugs will find one is darker than the other. Most of us also know that our bikes can at times behave like Prma Donna's when asked to idle nicely. Why is this? I believe I have the answer. With the ability to see what's going on inside the ECU and investing in a LM-2 dual channel wideband o2 controller with twin bosch 4.9 WB o2 sensors I can monitor the AFR of each cylinder simultaneously. Norton have mentioned at idle one cylinder will steal fuel from the other via the shared IAC pipe that connects both throttle bodies together. My investigations show cylinder 2 is not just stealing - IT IS COMMITTING DAYLIGHT ROBBERY! Norton said cylinder 1 robs No. 2, but my testing showed it's the other way round - but hey maybe they take turns! I know this because I can see the simultaneous AFR for each cylinder and if I add fuel to the lean cylinder's fuel injector it's the other cylinder that gets richer (and no I didn't get my cylinders confused)! The factory is required to sell its bikes with o2 sensors and this creates a problem. The o2 sensor looking after the lean cylinder keeps asking the ECU for more fuel, which of course goes to the other cylinder. The rich cylinder asks for less fuel which the ECU tries to trim until it runs out of adjustment. I know this because I 'switched on' cylinder 1's o2 sensor and watched on my laptop as the ECU added fuel until it ran out of adjustment. This can lead to one plug getting fouled (right hand cylinder) or at least darker than the other. If your bike spends a small amount of time at idle relative to normal running it won't be so apparent. Remember this is just an idle issue, once the throttle is opened up the IAC is out of the picture. This knowledge validates Richard-7's approach of blocking off the IAC pipe and instead setting the idle using the DO NOT TOUCH throttle position screw to crack open the throttle butterfly's just enough to achieve a stable idle. It's not perfect as you will get some fluctuation depending on engine temperature but you could argue it's better than doing nothing at all. There are other approaches I'm looking at but unless you have a programmable ECU they probably won't be helpful. I haven't finished fiddling around by any means, the fuel injectors are currently away being cleaned, flow rate and pattern tested (I expect there is nothing wrong but I want to make sure the bike is operating from a known reference point). To this end, it's got new plugs and the generic coil pack has been replaced with a bosch. For ease of fiddling the airbox has been removed and the throttle bodies have individual cone filters. This could make a difference so I'll be re-testing when the injectors are back in and the airbox refitted. My tuner has agreed to another mapping session once I've finished - I can't explore individual cylinder fuel trims under load without a dyno. In terms of where the engine ended up. The following graph shows the factory megaphone map compared with the current map. btw, these ECU's are incredibly complex with literally hundreds of settings! All to simply get a spark to ignite the right amount of fuel at the right time!