Check the ground wires at the intake manifold. Look at the wire connected to the sensor in the head under the front intake runners. Any bare wires means rotten insulation. If so, I'm suprised you have driven this long. I replaced mine several years ago and after I opened the black covers, most of the wires were bare.

You can either re-wire it or get a brand new one. There is one wire which goes from the harness under the intake manifold, under the front of the engine to the oil pressure sensor. If you get a new harness, there are yellow bands to indicate the clamp positions.
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Warren Bain - '86 744Ti M46 >290Kmi, '99 V70Glt > 45K mi, '96 965 >100Kmi Wifemobile near Manassas Va.. Check the 700/900 FAQ via the 'features' pull down menu.