Faulty lambda sensor? Can you test them?

Hi all.
Probably on the wrong forum because it's regarding my Alfa, but I recognise and value the wealth of knowledge and experience on here.
My 156 V6 coughed last week, and the injector light came on. It still drives and has normal power, but it's reluctant to start and lumpy first thing. The idle hunts a bit too when warm. It's generally not as crisp as normal.
Fiat ecuscan showed a low voltage to ecu error. I checked and cleaned the ecu to body and battery/body/ engine connections.
I cleared the code. No more have appeared, but the problem persists. I ran the car briefly with the lambda unplugged and it made no difference. Injector light is still on after half a dozen trips.
I've got the lambda off the car now. Is there anyway of testing it or should I just replace it as part of my investigations?
Thanks.
Ps It's more gutsy with the fuel too.

You can only test it in situ; it won't work until it's at high temperature. Even then you can only test it if the rest of the system is working; with an aftermarket AFR gauge or an oscilloscope you can check that, at hot idle, the system moves from just lean to just rich with around a one second period.

When the Lambda sensor dies, it tends to get slower and slower in its response; if it takes too long to indicate a change that the ECU thinks its made then it gets flagged as faulty and the ECU drops back to a mapped mode. The injection light remains on because this is an emissions failure.

Thanks (again) for a useful response, Barnacle.
My unplugging the Lambda and it making no difference was useless as a fault finding tool as I did it with the engine cold.
The car cycles every second or so when at warm tick over between higher and lower revs suggesting the lambda is doing its job.
I'm going to refit it and look at the maf instead.
Does a faulty lambda or maf throw up the injector light and or a code on, say, a 20v n/a Coupe, out of interest?
Thanks

Yes, it does, but you'd be better with startrek or similar to see what the active errors are.

Er, make that 'or similar'; startrek can't do the 159. MultiECU should be able to, but you might have to get the paid version.

I'm using the free version of multiscan, I guess that's why I didn't find what I needed.
I'll faff with the maf next.
Thanks

There is an old Alfa diagnostic called AlFadiag or DnEcuDiag its free but only shows codes and values not language but you can check the codes on Alfaowner.

Tip, When its loaded you need to select which ecu suits your car, just google it and im sure it will come up on Alfaforums.

Tom