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Discussion Starter #1
At any given time when listening to my car (at idle or cruising) you can hear a rapid and consistent fluctuation in rpms. The tach only shows about a 100-200 fluctuation but it is at a rapid pace (twice a second) and does vary in speed as the engine revs or if the A/C is on. When the A/C is on the rate of fluctuation slows down bit. My AED sounds like a miniature police siren with varying speeds, if that makes sense. This is also affecting my electrical system in that my headlights and interior lights rapidly dim and brighten. And is even noticable in the brightest of daylight. My CE light is on and has been for months, but for some reason any scanner that I have tried will not power on when hooked up to my car...with that said, I can't pull any codes to see what may be causing this or any other problem I may be encountering. Since whatever is happening is directly affecting my rpms, I am experiencing a semi-rough ride at low speeds (less than 30) and it feels like my car is being slightly tugged on, over and over.

Anyone have a suggestion? It doesn't seem like anything too major but it is definately a nuisance, and completely ruins the smooth ride that I am used to having with my last 2 T Birds. Not only that, but it's pretty annoying at night when you can see your headlights rapidly dimming and brightening.
 

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First, check the fuses under the dash. There is one labeled OBDII that is for the power to the diagnostic port.

Fluctuating idle is generally caused by a vacuum leak, an electrical problem, or a bad IAC valve or TPS. Check thoroughly for vacuum leaks, verify that the voltage is stable when the idle is fluctuating, and make sure the wiring to the TPS and IAC are ok. Check that the voltage at the TPS isn't moving at all when the car is idling. If it is changing and the throttle isn't moving, there is either faulty wiring or the sensor is bad.
 

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Discussion Starter #3
Thanks! I've already looked for vacuum leaks and haven't found any...but that doesn't mean they're not there. I'll look in to the other possibilities. Thanks again!
 
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