davland

My RAV4 is acting funny and the check engine light came on yesterday. When I am starting the car cold (after being off for more than an hour), I will turn the key, the starter engages the engine and the engine starts but immediately fails if I don't give it gas to keep the revolutions above 1000. If I keep applying gas for the first couple of minutes that the car is running, the problem goes away and the idle works. I know it's not the idle or timing because that works fine after a couple of minutes of driving. My Haynes manual suggests that it is either a gasket/ vacuum leak in the manifold, a fault in the fuel line, or a fault with the fuel injectors.

There you go. Who will take a bite? Any advice?

DEI37

Could be a vacuum leak for sure, that will set a check engine light. An oxygen sensor will as well, and will cause drivability problems. The only way to know for sure is to get the codes read. You can do that at a dealer. Could be a Mass Airflow Sensor, or Throttle Position Sensor...could be a host of things. Good luck...let us know what's going on.

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reconmike

sounds like either the coolant temp sensor is out of spec making the computer think it is warm when it is cold, you need to check the resistence of the sensor.

Or your idle air control valve is stuck, if you let me know by sat what year it is i can post the specs and how to check these items out

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davland

It's a 98 RAV4, front wheel drive. Thanks for your help guys.

Sion

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.

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