check the 02 sensor.BRITTLE WIRES.
i would check all the wiring for sure.here is how weird wiring can be.i had a guy bring in an alpine 240 watt amp with a blown right side .only blows when he turns a left hand corner.IMPOSSIBLE I SAID.
AFTER Ibench test with a dummy load ,unblowable.he puts it back and blows it up again.after i fix it again,( this time i put a 5 amp fuse in series with the speaker wire)i install it and sure enough ,turn right ,ok......
turn left,it blows the fuse.turns out that one of the original dash wires got pinched in the heater control,and would touch and ground out,shorting the outputs to ground. SO WHAT I AM SAYING IS ALWAYS CHECK THE WIRING CAREFULLY FIRST.