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Sion · 06-28-2003, 01:47 PM

I agree with reconmike, sounds like a temp sensor. when a vehicle is started cold, it starts in what is called open loop, which means that it is operating without help from the various sensors that allow the computer to calculate the best air-fuel mixture. during open loop running, the air-fuel mixture is enrichened so that the engine will keep running while warming up (this process replaces the old manual choke method). As the engine warms up, the computer monitors the temp of the engine (via a coolant temp sensor in the block or intake manifold) and once a certain temp is reached, the computer switches into closed loop functioning. In closed loop, the computer accepts input from the various sensors to calculate optimal air-fuel mixture.

in this case, it sounds like the temp sensor is telling the computer that the engine is warm when in fact it is not. thus the computer is going into closed loop immediately upon starting. an engine runs much better when warm than cold, and in this case the computer is not compensating for the cold engine by adding more gas to the air-fuel mixture. thus the symptoms you describe.

note: something to remember about sensors - they are not always bad, even if pulling the diagnostic code from the computer suggests that the reading is out of whack. many times, there is ANOTHER problem which is causing the reading to be out of specification.

for example, if the O2 (oxygen) sensor reading is out of spec, it could be a bad sensor, OR it could be a bad spark plug. how so? well, if one plug is not firing, then there will be unburnt fuel going directly into the exhaust (but the engine will still run, albeit poorly). this will adversely affect the reading that the O2 sensor gives the computer. the computer will turn on the check engine light and if the trouble code is pulled, it will say something to the effect of "O2 sensor reading out of range". But that does not mean the sensor is bad. In this case, it actually means that the sensor is doing its job correctly, but that there is another problem.

now, in the case of davland's Rav4, I do think that the sensor is bad, but another possible cause could be that the coolant is dirty and is interfering with the sensor's ability to correctly monitor the engine temp. however, I doubt that would cause a false warm engine temp.

06-28-2003, 01:47 PM	#5 (permalink)
Sion Dumb all over...a little ugly on the side Location: In the room where the giant fire puffer works, and the torture never stops.	I agree with reconmike, sounds like a temp sensor. when a vehicle is started cold, it starts in what is called open loop, which means that it is operating without help from the various sensors that allow the computer to calculate the best air-fuel mixture. during open loop running, the air-fuel mixture is enrichened so that the engine will keep running while warming up (this process replaces the old manual choke method). As the engine warms up, the computer monitors the temp of the engine (via a coolant temp sensor in the block or intake manifold) and once a certain temp is reached, the computer switches into closed loop functioning. In closed loop, the computer accepts input from the various sensors to calculate optimal air-fuel mixture. in this case, it sounds like the temp sensor is telling the computer that the engine is warm when in fact it is not. thus the computer is going into closed loop immediately upon starting. an engine runs much better when warm than cold, and in this case the computer is not compensating for the cold engine by adding more gas to the air-fuel mixture. thus the symptoms you describe. note: something to remember about sensors - they are not always bad, even if pulling the diagnostic code from the computer suggests that the reading is out of whack. many times, there is ANOTHER problem which is causing the reading to be out of specification. for example, if the O2 (oxygen) sensor reading is out of spec, it could be a bad sensor, OR it could be a bad spark plug. how so? well, if one plug is not firing, then there will be unburnt fuel going directly into the exhaust (but the engine will still run, albeit poorly). this will adversely affect the reading that the O2 sensor gives the computer. the computer will turn on the check engine light and if the trouble code is pulled, it will say something to the effect of "O2 sensor reading out of range". But that does not mean the sensor is bad. In this case, it actually means that the sensor is doing its job correctly, but that there is another problem. now, in the case of davland's Rav4, I do think that the sensor is bad, but another possible cause could be that the coolant is dirty and is interfering with the sensor's ability to correctly monitor the engine temp. however, I doubt that would cause a false warm engine temp. __________________ He's the best, of course, of all the worst. Some wrong been done, he done it first. -fz I jus' want ta thank you...falettinme...be mice elf...agin...