Silly guess: If the knock sensor is sending "KNOCK!" signals even when it's OK, and the computer just responds blindly, I can see it keep retarding the timing till it slowly dies while sitting at idle. The base timing being way off to start with wouldn't help any.
Makes as much sense as anything else to explain what happened.
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Sensible or not, replacing the part ended the problem.
I thought about a false "knock" signal from the sensor, which is one of the reasons I wanted to know the model year and engine setup. If the car has a distributor-less ignition, then base ignition timing is probably pre-set with no adjustment possible. If the car has a conventional distributor with electronic timing advance, then there is a physical limit to how much timing can be retarded or advanced. The rotor's arc has to physically fit between the contacts in the distributor cap. Whatever base timing is set, at base timing with no advance, the spark would be sent through the rotor towards the end of the rotor's contact with a particular terminal, and as timing is advanced, spark is sent towards the beginning of the rotor's contact with the terminal. IOW, with this setup, timing cannot be retarded past base timing, unless the system is designed so that base timing is set as advanced as possible and use engine knocking to retard timing. I would think this arrangement would not be good for the long-term life of the mechanical components in the engine. Regardless of the setup, I would think the root cause of the problem would have to be incorrect base timing, not a false signal from the knock sensor. A bad knock sensor would be a secondary problem, not the root cause.
The other thing that has me puzzled is the nature of the knock sensor. Toyota uses a piezo-electric crystal inside the knock sensor, and the crystal is struck or twisted, a static spark is emitted. I don't know much about those crystals, but I can't imagine how they can send a signal without a physical force, i.e., knocking, exerted on them. An open circuit would be no signal to the ECM, and in the absence of voltage from the crystal, a short circuit would do nothing, unless voltage from an exterior source is somehow getting into the pigtail between the crystal and the connector to the wiring harness.
AFAIK, you are correct. The mechanical energy of deformation becomes electrical energy. No change in deformation, no spark.
Possible useful data: IIRC, the source impedance of the piezo/e crystal is very high. A large serial resistance could probably be tolerated (guess: several tens of kilo-ohms); but it wouldn't take much shunt leakage (ie, across the wires carrying the pulse away) for the pulse to be crippled. Think of a battery with high internal resistance -- but _really_ high.
Excessive shunt capacitance would also slug the pulse -- though I don't see how anyone could _accidentally_ introduce that into an established design. OTOH, if there were significant extra serial resistance, such from a manky connection, less shunt capacitance could slug the pulse. Shunt capacitance could be caused by using a non-standard cable, especially screened and excessively long. NB: This paragraph is speculative; it may also contain nuts.
This info seems to make it even less likely that the bad knock sensor would make the ECM retard timing. In other words, a bad knock sensor is more likely to keep timing too advanced, not too retarded.
the needle will move up. But always reads cold when driving. The coolant is about two years old, also, but the temp gauge read cold even after new coolant was put in.
to see if it is stuck or something
If the temp gauge reads cold and there is no heat from the heater, then the most likely cause is a thermostat stuck in the open position. If you do the repair yourself, get enough new coolant for the capacity of your cooling system, a new thermostat, and a new thermostat housing. Take the old coolant to an appropriate recycling or waste disposal facility. Carefully clean the surfaces where the old gasket was with a gasket scraper or razor blade, being careful to avoid gouging the aluminum housing. Orient the new thermostat exactly the same way as the old one, with the spring facing down and the jiggler valve oriented the same way as the old one. With the heater control in the full hot position, re-fill the radiator, leave the cap off, and start the engine. Watch the coolant level in the radiator, and as it drops, slowly top it off until it does not drop any more. Replace the radiator cap and fill the coolant overflow bottle to the hot mark. Watch the overflow bottle over the next few days and top off as needed.
If you elect to have someone do the work for you, ask for the old thermostat so you can see what it looks like when it is stuck open.
It sounds more like the thermostat is stuck open.
Good luck!
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