RPMs drop when turning steering wheel at stop

I can re-produce this problem every time. Has anyone seen this, can it be fixed as a 'do-it-yourself' kinda project?
I have a year 2000 Ford Focus SE. If I put the car in park and turn
the wheel just a little to the left or right, the RPMs drop and it feels like the car is going to stall but it doesn't. This started happening about 2 months ago. Is there a sensor that knows when the power steering is in use and maybe the sensor is damaged and not telling the engine to compensate by raising the RPMs?! I've also noticed it by driving down the highway and going from 65MPH to a dead stop, all while maintaining a straight line and as my car comes to a stop, the RPMs drop again. The >latest< recall replaced the fuel filter so I guess that can be ruled out as guilty. :)
Any ideas?
On another note.... when should I change my factory spark plugs? (car currently has 55K miles)....
And something else.... I've noticed that on my battery, one of the terminals has that white chalky powder building up around it. Is this a sign the battery need replaced? I had this problem on a '94 Probe and had to replace the battery AND the wires. The mechanic explained it to me but it was some weird answer. Something about the wires building up resistance (or something like that) and even with just a new battery, it would happen again he said.
Oh well, any help appreciated!!
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Your car has power steering. The power steering pump is engine driven. When you turn the wheel at tickover it makes a demand on the pump which drags the revs down. The EEC senses the drop and increases the revs again to the correct RPM. You can reproduce the same symptoms by turning the lights on and off at idle RPM.
--
Paul Giverin

British Jet Engine Website http://www.britjet.co.uk
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I think then that this EEC? is broke or something. Because when turning the wheel at a dead stop, the RPMs drop and do NOT come back up unless I stop moving the steering wheel. The engine is not compensating from the demand the power steering pump is placing on it. Is this something I can fix or should I take it to my dealer or just keep on motoring and ignore it?
writes

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It sounds like your idle air bypass valve is not working properly. It is located on the intake manifold and is hard to get to on the Zetec. I used to remove and clean the one on my Escort when it had this problem. It might not be getting the right electrical signal from the computer either, but more likely it just needs to be cleaned or replaced. WHAT IT DOES: 1) Fast idle...It passes air past the throttle to rev the engine at idle when it is cold. 2) When a load is put on (like your power steering/AC, etc, it maintains a normal idle speed. When it is working ok, the idle will be pretty stable when turning the wheel, putting on the AC, lights, etc. You can try disconnecting the battery for an hour or so to have the engine "re-learn" how to idle. Worth a try.
As to the battery corrosion, you do not likely need a new battery. Put on some latex gloves as the acid is nasty and take off the terminals. Soak the terminals in a baking soda paste solution (add water) and neutralize all the white deposits. When the bubbling stops, rinse with clean water. Clean the battery top and dry. Don't get baking soda in the battery, as it will weaken the acid strength. Dry the terminals and clean the contact parts of them until shiny with a battery brush from an auto parts store. Put the terminals back on, tighten and coat them lightly with petroleum jelly to retard future corrosion. Don't overfill the batterey with water (distilled only) as this causes acid vapor to blow out of the vents and you will be doing this again.
Gary
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gmzx3 gave you good advice, but I just wanted to add that it really is not such a good idea to turn the steering when not moving at all. Just because the power steering allows you to, does not mean it is not harmful. It puts lots of stress on the steering, suspension, and the unibody. It is better to be rolling slightly as you turn the wheel.
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Yep, couldn't agree more - one of the real problems with power steering is that people developed this bad habit. It's next to impossible in a non-PAS car, so you had to rotate the wheels slightly.
My mother always does this, and there are rubbed patches all over the gravel road overcoat outside her house where she's done it and ripped the gravel off the tarmac.
A worse crime is turning the wheel to full lock and causing the pressure release valve to go off - my mate does this all the time and wonders why his power steering was knackered on his old car!
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