I have a 96 4.6 SLS that surges almost all the time only when the outside temp is above 70 degrees. I've searched posts and found good info telling me that surging can be remedied by cleaning the TB and checking and cleaning the ISC valve. But before I do all that I was wondering that since it almost never happens in the winter and only happens on warm days (every warm day, every time I drive) if that then means it's something other than throttle-body buildup or the ISC valve- I get no special error codes-I do sometimes get an Emissions message in the info panel.
Foot on the brake at a red light 1,500-2,000rpm, throw it in park and it jumps to 3,000+rpm- a/c blows cold when not surging, blows warm when surging. Sometimes shutting down temporarily alleviates the problem, but it always comes back. Thanks for any ideas.

Surging is often caused by a vacuum leak. Since your A/C seems to be affected, check all the vacuum lines under the dash, at the parking brake release and cabin supply line at the firewall. Also, trace the supply line back to the reserviour canister and check it for cracks or broken lines.

Many thanks Ranger- that makes sense and it leads me to be more optimistic about investing some knuckle time