Toyota Repair: engine hot, revving oddly, coolant temp, coolant leak

Question
92 4wd xtra cab truck - the engine started revving by itself very quickly, it will rev up then down about once a second.  this morning i noticed the it was running hot so i suspect the thermostat.  sound right?


Answer
The engine is low on coolant, there is probably a coolant leak so check for that, the reason the idle is erratic is that the ECU coolant temp sensor gets air passing by it instead of coolant,ie: hot steam, when the computer sees this high temperature it turns the injectors off and then back on again, again, look for a coolant leak or other cause of the low coolant level.