You should listen to me. No, seriously, listen to me.
Join Date: Oct 2008
Location: Santa Barbara
Motorcycle: Blue 2006 GSX-R1000
Re: GSXR 1000 K5 lumpy idle and stalling
+1 on throttle body cleans being in the same category as engine oil flushes for cars. Unless your TB is filthy, inside and out, it sounds unnecessary. If it is filthy, the entire engine likely needs a cleaning.
Changing the plugs is a way to learn about working on the bike. But there's a fair chance that they're OK. Suzuki recommends replacing at 7500 mi/12000 km. You'll need a spark plug socket and a torque wrench unless you use the tightening angle method. Beware of antiseize, i.e. don't torque if you use any.
A PC & tune is appropriate if you're replacing the entire exhaust. But if you're just adding a slip-on to the OEM headers, it shouldn't be necessary. However UK/EU models originally had a muffler with a cat converter and a different ECM. The ECM difference is generally associated with the immobilizer. But there's a possibility that the fueling maps are also slightly different and a PC may be appropriate (that may explain why the Australian models, which have an immobilizer but no cat, got a different ECM). Note that a dyno tune will optimize power at the expense of gas mileage. Also note that, though you can get away with it right now, there may come a time when a removed cat will be a MOT fail (as it is on cars right now).