Question about 1990 Ford F150

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Map sensor Okay, I know what the map sensor is now. There is also a diagram under the hood that shows vacuum hose routing, and it shows map on the right front fender, but I didn't know what it was. (My truck runs and idles, but when I start to gain a little speed, it keeps cutting out). I unplugged the map sensor like you said to, and it slows way down, and then surges up and down. When I plug it back in, it runs normal again. You said earlier that if there were any changes when I unplugged it, the sensor was bad, but shouldn't it run differently if I unplug it?

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  • Harley Sep 11, 2008

    vehicle is running again

  • Harley Sep 12, 2008

    keemo; I've got my truck running again, but I'm trying to learn something from you here. I don't quite understand your last statement. When you said "however, with it plugged in it acts the same way which it should not", do you mean that if my problem is that the sensor is bad it will act the same way plugged in that it will act if it was unplugged, and it shouldn't be like that; or that if it's bad, it will start acting just the opposite of what I want, which would therefore be acting just like I would certainly NOT ever be wanting it to act? I appreciate your help and time, Thank You


  • Harley Sep 12, 2008

    keemo; Thanks for the reply, but now you really have confused me. Which one of my two conditions I was asking you about do you mean?

  • Harley Sep 12, 2008

    Thanks. Now I know the answer as to what it will act like IF the sensor is bad. I don't see why it would ever just be unplugged for any reason, the connector's not going to just fall apart some day on it's own,so that scenario is out of the question, and obviously I know how it acts if it's not bad



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That is not a map sensor(mass air flow) it is a barometric switch also know as a mps(manifold pressure sensor) if your vehicle idles fine but when you try to accelarate. i have a question? is it a throttle body or a carburator type fuel system?

Posted on Sep 01, 2008

  • 1 more comment 
  • Ronald Mueller
    Ronald Mueller Sep 12, 2008

    the map sensor regulates the air pressure in the intake if you unplug it the vehicle is suppose to act just as you described,however with it plugged in it acts the same way which it should not

  • Ronald Mueller
    Ronald Mueller Sep 12, 2008

    I apologize for not being clearer,but yes that is what i mean about the sensor

  • Ronald Mueller
    Ronald Mueller Sep 12, 2008

    ok if the map sensor is unplugged the care will idle at diferent rates(high/low) constantly. now if the map sensor is plugged in and the sensor is defective the car will idle the same way. you should always have a steady idle with a good map sensor. I hope this clears some of the confusion. please change the rating thanks.



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Would appear that you have either a bad MAP sensor, or a leaking vacuum line somewhere.

The bad readings from the MAP sensor will cause the trouble code with the oxygen sensor (and the reason why you failed the test,) but this is not to say that the oxygen sensor can't be bad also.

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