1997 Lincoln Town Car: engine surges

I've got a 1997 Lincoln Town Car, Cartier Series. I notice that when idling in the Drive Gear, the car sometimes surges ahead, occasionally with force a bit stronger than
the force with which I've got the brakes holding it back. And sometimes, the engine dips really low, almost to the point where it seems like it's going to stall, which thankfully it doesn't.
One other pattern: the car only does this when I've got the heater or A/C on.
What could this be and how might I repair it? I took it to Midas and they adjusted the idle, which helped but didn't ultimately solve the problem. TIA.
-The Derfer
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There IS no adjustment to the Idle Air control. What they PROBABLY did is either adjust the throttle stop screw... a NO-NO.. or spray some intake cleaner in the IAC.
NEVER LET THOSE MONKEYS under your hood.
If you have some metric wrenches, you can go to NAPA, get the part and replace it yourself. I dont recommend cleaning it. Effect wont last long.
While you are at it, you might google on how to clean your Mass Air Flow sensor. Needs done periodically, never mind what Ford says.
--
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
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The Derfer wrote:

Clean or replace IAC valve. Take it to someplace like AutoZone where they'll pull the engine trouble codes, for free (except Caifornia).
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