Running Issue when cold

Hi all. Not sure if anyone can help. I bought a 2010 Stelvio 1200 a month back it's been rollered and ran fine but I decided to strip bodywork off and clean and sort some bits plus rear shock linkage and a few other bits. I removed fuel tank and bodywork and battery. All back together and I have checked the plugs and connectors over and over. Bike will start but takes a bit of cranking once it starts it's lumpy and if I try and open the throttle it will pop and bang.
If I leave it to get warm 6 or 7 mins it then runs perfectly!
Any help gratefully received as meant to be going to Germany on the bike in a couple of weeks
Thanks.

Is the stepper working?

Hi Pete
So over the weekend I went through some bits to try and eliminate stuff. So on Guzzi Diag initially the stepper motor was showing me readings but didnt seem to change much plus when running if I started and stopped stepper on Diag it didnt seem to affect tickover? When I turn ignition on it make a short buzz and when I turn off I get a long noise as if it is working? I have swapped out the temp sensor in case it was faulty but it was reading ok via diag as well so probably not that.

OK, if the plug caps are not arcing it would seem to be definitely temp related but I would do two easy checks.

1.) Run a compression test on each cylinder. Throttle fully open, just disconnect the coils, (This will give a service warning but that is normal.) and crank it over for five seconds. DO NOT leave the other coil connected! You should get a figure of around 175PSI both sides. If one side or the other is much higher than the other it is likely to be....

2.) Check the cam timing.

Thanks will check these later. Is there also a way to bypass the stepper to rule the stepper out?

No.

As I've mentioned, plugging the inlet to the stepper is the best way to test if it either partially blocked or leaking somewhere.

If it's partially blocked, then plugging the inlet will effectively disable it. If it's leaking, there'll be no change.

I checked the comp and timing last night all good. Comp 180psi , I cleaned stepper out with fuel cleaner and refitted. I will try again tonight and block inlet to see what the outcome is. Thanks

[You must be registered and logged in to see this image.]
So I blocked the stepper and it made it worse. I've also fitted a new Bosch equivalent temp sensor just in case. What I have noticed it literally only lasts about a minute or two know. But where I thought it was running perfect when hot ! Well it sounds great blipping the throttle and at idle but if I hold it at 3500-4000 rpm you can hear it slightly popping and missing not smooth. I took some shots from Guzzi Diag? . Thanks

Hi. Firstly thanks for everyone's input. It was indeed the stepper motor playing up. I have lubed it and used bike regularly and everything is pretty much 99% Odd hiccup when cold but more or less there. I will keep an eye out for a replacement stepper. Thanks