The Innovate LC-1 is quite sensitive to ground induced voltages affecting the Lambda reading. Some people have seen the AFR's out by 0.5 to 1 depending on how bad it is. You should wire the Innovate LC-1 ground wire to the analog ground the ECU uses, and make sure that is a good ground as well. Any voltage on the analog ground wire will alter the output of the DAC chips on the Innocate LC-1 controller and give an off reading.

You should check the digital reading (from laptiop/PC connected to the serial line) against the analog output and check they are the same. When I first wired mine in I had an offset of about 0.1 V which was enough to throw the readings out a bit.

It's also worth noting that if you get misfires at higher RPM's then the inciomplete combustion will show as lean, as the oxygen content in the exhaust will be higher - remember these sensors measure unused oxygen content - not fuel.