The temp sensor you are referring to tells the lambda computer that the engine has warmed up and can now trust the 02 sensor. It will then modulate the fequency valve. To test the temp sensor remove it, hook up a continuity tester, and heat the sensor in some water. At some point before 212 it should change state. If it does not then you can assume it is defective. You cannot tell by ear what the frequency valve is doing execpt that is doing something. To see what is going on hook up a dwell meter to the diagnostic plug. David Teitelbaum vin 10757 --- In dmcnews@xxxx, Delorean17@xxxx wrote: > 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