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No Acceleration And Check Engine Light When Cold


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Has someone had a similar problem and knows the solution?

On my LX-470, 1998 model, when the engine is very cold (sub-freezing) the car does not accelerate and the check engine light comes on with error codes p1121 and p1120.

Here is what I have done:

1) I cleaned the mass air flow sensor. This had no effect. The readings from the mass flow sensor are 5 g/s (0.7 lbs/min) at idle and 30 g/s (4 lbs/min) at 4000 RPM. Anyone know the normal range for this?

2) I then found that when I heat the throttle body (on the side where the accelerator cable is attached to the accelerator pedal position sensor) with a hair dryer before starting the car, the problem does not occur.

3) Using an OBD scan tool attachable via USB cable to a laptop (cool gadget, $60 on Amazon), I find:

The "absolute throttle position" output at warm temperature is: 15% for accelerator pedal released, 80% for pedal pressed down, while at cold temperature it is 17% for pedal released and 21% for pedal pressed down. All with engine off.

This looks like a defective sensor. However, there are two sensors on the throttle body: a throttle position sensor ($140 on Amazon) and an accelerator pedal position sensor ($299, only available at Toyota or Lexus). Unfortunately, the scan tool output is only for the "absolute throttle position", and it is not clear to me which of the two sensors are monitored.

Thanks for any advice,


1998 LX470

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