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Several problems... Related?

I’m having several problems, and I’m wondering if they are related:

  1. Sometimes the heat/ac/vent blows on the windshield instead of where they are supposed to be. Occaisionally it works at first, and then changes after a few minutes to blow onto the windshield.

  2. Sometimes I get a buzzing sound under the hood. Usually when I’m stopped, but sometimes while moving. The car idles high when this happens. If I tap the accelerator, this usually stops the noise and the idle drops to normal.

  3. This morning, the brake warning light kept coming on while using the brake. The fluid level and pedal are OK, and the car stops OK. Then the buzzing sound came on, the engine light came on, and the brake warning light went out at the same time. The brake light hasn’t come on since. The scanner tool indicates the IAC was running too fast.

They are related, you have a vacuum leak. Usually you can hear a high pitched whistle when you get close to it.

What year is this Grand Marquis?


@keith is correct, sounds like a vacuum leak. Mechanics have a systematic way to test this, going through each vacuum controlled device one by one. This is a common problem and they do it all the time. While easy to diagnose, the fix might prove expensive, especially if the problem is one of the vent door vacuum-motors under the dash. These are often vacuum controlled. The only puzzler is the brake light. hmmm … Since the brake booster is a vacuum powered device, I guess a vacuum leak could turn on the brake light. It might well be your brake booster has simply sprung a leak, easy to fix. But it is possible the brake light is unrelated. You may actually have a problem-in-progress with the brake hydraulic system, or w/some cars the brake light can come on when something critically important to safety or drivability (other than the brakes) fails, like a failing alternator.

Today, the “check engine” light was on all day. The buzzing sound has not occurred at all, and the brake light has not come on. It’s as if the brake light problem and buzzing issue suddenly stopped the instant the engine light came on.

It’s a 2002.

I suspect you have a P0171 lean fault code.

Please post back.

Have you opened the hood and listened for obvious vacuum leaks, as the other guys already suggested?

It was P1506, if I remember correctly. I have since fixed two of my problems: Added brake fluid, and replaced my idle air control valve.

Did the code go away?