I tested my last AFM by the book, and (if I remember correctly) the signal wire had really high resistance. So I took the thing apart like you are not supposed to do and looked at it. It looked ok. So I got out my two spare units and both were bad as well. So I went back to the open one and fiddled around with it. I found that the wiper arm that sweeps across the trace board had poor contact. I took the wiper off, put a slight bend at the tip, and cleaned the top with some emery paper. Put it back together, good as new. Just that alone dropped .5% CO on the smog machine. Anyway, that saved me loads of dough on a newly rebuilt AFM.
