I have the same issue with my 1996 Geo Tracker 1.6 16V Automatic 4x2, and have run the gauntlet on trouble shooting. Once I clear the code, it comes back within about 1/2 a second of starting the car. I've ohmed out the wires to the ECM (fine), checked them on the oscilloscope (5-6V signal is consistent), I've bypassed the old wires and rewired (no change), replaced the sensor (no change), shaved the sensor down to get closer to the tone wheel (no change), removed the oil pan gasket (no change), checked the timing at idle and at running temperature (-2 to -5 TDC at idle), checked alignment of the timing marks when not running (-1 TDC when cam notch/dot is aligned), check the tone ring (6 teeth). The car runs great, no problems, just this stupid P0335 code. Has anyone figured this out? What solution did you use or run across. I'm at my wits end and I can't get a vehicle inspection due to this code.