98 Taurus - Idle problems

My 98 Taurus with 86K has an idle problem. If Im idling with the heat or air on the rpm's drop to 400-600, but not every time. Also at highway speed I notice it bog down periodically. It maybe when the compressor
kicks in and out. Could this be the IAC? I don't know if this is related, but at highway speed the lights may dim, again sporadically. I checked the alternator and it is putting out the correct current. I did find an alternator brace that was loose. Maybe that was causing the light dimming thing. Any thoughts?
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baldone48 wrote:

take them off, clean them and torque them back down.
The IAC would not affect hiway speed. But if your in doubt take it off and clean it out with carb cleaner or such. Change your fuel filter too for good measure. You might have a plug wire going bad too. If you don't have coil on plug ignition, start your car at night with the hood up in a dark area and look closely at the plug wires for signs or arcing.
Bob
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Thanks for the info Bob. I had already checked and replaced my negitive battery cable because it kept getting a white powder on it. I didn't know if that was a symptom of something else or another problem. I checked all the connections and fuses. I originally thought the problem maybe the alternator or regulator. I also had taken off the IAC and sprayed cleaner in it.
I replaced the fuel filter today. I don't think I had since i've had the vehicle. I will look at the plug wires.
Thanks again, Dave
I
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