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Check coolant temp sensor. These fail often and cause all kinds of mystery problems. This unit acts much like a choke on old carb engines and can fail in different ways. Most common (I think) they fail such that the ECU thinks the engine is cold when it has begun to warm and thus the ECU delivers too long a pulse to the injectors so that the engine runs way too rich. I think it is also possible for the sensor to fail at any point between cold and warm such that the fuel mix is wrong except for the particular temp at which the sensor is stuck. Also O2 sensor has some fuel "trim" input.
Please do the following.
- (Reset memory) Remove the negative battery terminal for 30 Seconds, reconnect and start the engine. If problem persists,
- Check the resistances of high tension cords (DMM Range = 100 K, Resistance - 10 K Ohms- 30 K Ohms).
- Check the distributor cap, rotor for any crack or corrosion, and module.
- TP position sensor, and MAP sensor.
- Check vacuum hoses and intake manifold for air leakage.
- Check Idle air control valve.
- Check spark plugs gaps.
Ok, it sounds like that the timing is retarded and needs to be advanced. Now when you say revs up and down, is this happening only at idle? Do you happen to have a manual for your truck? If you do, remove the idle air control (IAC) valve and clean the inside of it out. It may be carboned up. With carb. cleaner, clean the inside of the throttle body out. You may see a bunch of black soot looking stuff come out of it. Keep spraying the carb. cleaner until it's comes out clear. Advance the timing 2 to 4 degrees, this will get rid of the "no take off from a dead stop" issues. Get a manual, so you can see how where the components I'm talking about are. Let me know how things go.