lambda sensor switch

[Delorean17@xxxx]

Hello List,
When I purchased my car the ground wire to the lambda switch(switch 
located on cooling manifold) was disconnected. When I hook up the ground 
wire like it should be the frequency valve starts up and will not stop, even 
when the engine is hot. would this indicate a bad lambda sensor switch? 
what else should I look at? I have the whole intake off now so I would like 
to change the switch now if it is the problem.

Thanks
David