Just an FYI if it applies to your vehicle/ symptons- couldn't figure out why my 91 4.0 YJ would idle about 1300-1400 as I rolled to a stop, and then back down to normal idle within about 3 seconds consistently. Vacuum leaks were pointed out as a potential cause- couldn't find any. Changed every sensor/ and cleaned throttle body while I was at- no difference. Once in a awhile it would stumble accelerating from a stop and if I didn't catch it in time, die when there were a ton of cars behind me.
Last time it died on me (and it was a pain in the rear to start anytime it did this) I got ****ed and took it to the dealer, just tired of messing with it. Turns out it was the pigtail going to the coolant temperature sensor. They cut it out of the wiring, spliced the new connector/ wire in and voila, runs like a champ!
Idle is now perfect all the time, never stumbles when accelerating, and starts better. All for a piece of wiring that looked fine.
Just thought I'd throw that in for any help to people having that kind of symptom. You guys have helped me with questions, figured if I can save anyone else the trouble I went though, that's what this is about, right?