2002 Mercury Sable Intermittent rough idle

Thank you

idle should adjust up as and when AC or a load on
suspect IAC valve (very common)
remove IAC valve clean or replace
if have check engine light on
have it scanned for codes most local parts store can help you in getting the codes

Purchased and installed a new IAC valve. Ran the car around the patch a few times to get the temp up. The first time I came to a stop with normal temp + A/C, the RPM dropped, came up, dropped again. Thinking the computer was still learning I took it out for a spin and all was well. Wife took it out and still OK. Just had it out and after it sat for an hour it was again rough when started, then OK during the ride home. So it's 90% better, but not asymptomatic. Thoughts?

P.S. I did NOT clean out the intake with the IAC off. If I should have, what's the best way?

Check for any vacuum leaks
scan for codes

So the problem got a little worse and the engine light came on. Took it to the dealer. Said the No.2 cylinder was coming up on the codes. Plug was fouled and cable in bad shape. Never changed plugs so I had them replace all 6 and new cables. Now it idles to the point where you don't have to hit the accelerator. Place it in park and the RPM races. Dealer telling me the IAC I put in is probably bad and they want to put in a Motorcraft IAC. I'm not sure I buy it. The engine would have responded this way even with No.2 plug bad. Ideas??

Most common two reason for high idle , other than mechanical is that a bad IAC or a vacuum leak

Followed your IAC guide. Removed the IAC and hooked up the wiring. Turned to "On" position. I could hear and feel a 'pop' coming from the IAC motor, but the IAC itself did not move in either direction.

If its new return it as defect if old clean it and try or have it replaced

I screwed the pooch and threw out the box and receipt. Oh, well. Thanks for your prompt replies.

check with the store , some use electronic recordes ,and they may have yours
good luck