If the voltage is good at the battery terminals while its cranking, but the starter is spinning slower than it should, the next step would be to put the meter on the starter terminals and see if the 12V is still there while cranking, or if you are losing it somewhere between the battery and the starter.
Im dont know where those terminals are on an 1100 - someone else will have to jump in with that info.
check engine light is on and blinks 3 times, break, repeat. Manual says tps sensor...
I forgot to mention, if your battery is going dead to the point that it wont crank the starter, the tps sensor fault code could just be from trying to run on low voltage.
If the bike runs ok when you push start it, and you dont get that check engine light, then your tps is ok.
If your battery checks out ok, then the tps is something to look into - because the ECM changes the timing based on where the TPS is. Its a simple thing to check.
This is a good time to mention: the factory service manual for most vstar bikes is on the internet somewhere in pdf format. If you dont have one google Vstar 1100 service manual, and you might be able to download it for free. There is a page for checking the TPS with a volt meter.