I have a 99 OBS with 290K miles and AT. The car has been running great as I take good care of it. Then one day after adding oil the CEL came on with "Faulty Knock Sensor". It would randomly retard the timing, then run normally. It's a recently new sensor but I changed it with a cheapo anyway. Same thing, so I tried a different one. Swapped the ECM, sea foamed the engine, new spark plugs, oil change, new pcv valve, adjusted my valves, even moved the knock sensor to the hole back and to the right of the original knock spot. There's no CEL now but it will still randomly go into limp mode and then come out of it strong, and then lose some of that extra power. I really want to get this fixed for sentimental reasons and because the engine is still very strong.