On my 1994 850T I have had the front knock sensor replaced with the new wiring harness. The cel comes on for a month, off for a month or so, etc. I figure it is a flaky connection where the wires connect to the harness. Has anyone had this same symptom? Where should I look to clean/tighten connections. Car runs fine otherwise.

Unfortunately, the knock sensors are under the intake manifold. If a garage did this for you, let them know that positioning each sensor is critical. They can use a mirror to see if they are in the correct position.
I doubt that the plugs are at fault, that would trigger a fault immediately, not monthly.

Klaus
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Just driving a 1998 V70R :)

Thanks for replying. The weird thing is that it will be OK for months and then the light will come on for say 1 month. Then it will go off again. I am thinking that the wiring harness has a intermittent connection and due to water getting in or temperature change the signal gets cut off. They did use the later harness.

The new harness is better than the old one. When the CEL comes back on, drive it over to the shop and let them check it out. If it is a loose connection, they can blindly reach down and make sure it is connected tightly.

Klaus
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Just driving a 1998 V70R :)

The cel is on now, has been for on for a month. When I have time I will bring it to mechanic.