Ford: idling control senser, egr valve, ford taurus

Question
I have a 99 ford taurus.  When I start the car the rpm's will usually register around a l-without using any gas.  On some days, I have to continually give it gas to keep it from shutting off.  I know very little about cars but think it might have something to do with the idling control senser.  There are also times when I will be stopped and get a surge and have to keep my foot on the gas to keep it from shooting off.  Does this sound like it could be the idling control senser and if so how much is it to replace and how difficult is it to replace.  Thank you for your help. I just replaced the alternator and had a new egr valve put on 2 years ago.

Answer
Nancy did this problem happen after you replace the alt? if so did you disconect the battery? if you did then all you have to do is disc the battery agan and wait 20 min. and rehook it back up.what the vehicle is trying to do is set it's idle strategy . now the idle air speed controler or we call it IAC valve.may be the problem it reseting the comp.now if redoing  the battery doesn't work.also what i want you to do is remove the throttle body hose and look inside to see if it dirty if so you have to clean it out this will cause your vehicle to stall out . do these things first and let me know what happens.