06 manual. Car was jerky at low speeds so I replaced the APP sensor eight days ago and it was buttery smooth. Not sure if that's relevant but just some background info.

Today it's idling high. 79 degrees out so not that hot. Car has been warmed up and driven; idles at ~1200rpm with the AC on, ~1050rpm with the AC off. Both are higher idle points than usual and I also don't undetunder why it idles higher with the AC off, I'd expect it to be the opposite. When I first got in this morning the idle revs were jumping around a bit, seemingly randomly.

Thoughts?

 

After posting the idle went back to normal (~800rpm), then back to high as described above, and now back down to normal again.

 

disconnect battery for a few minutes and reconnect. Put the car in ACC mode and turn everything off such as radio, lights, etc. Turn car off and then start. Let it run until the cooling fan cycles at least 2 times and the idle relearn procedure will be done. A weak battery can cause the ECU to loose it's idle and have it dip to around 500 RPM

 

I'll give that a try, although my problem is not that the idle dips too LOW, it sits too HIGH. Just now after it warmed up the idle was at 1200-1500, lower with the AC on, higher with it off. Very strange.

 

Riddle me this: my O2 sensor and EGR aren't ready to test so I can't pass inspection. They were mysteriously reset at the dealership but since then I've driven 300mi or so and it still said not ready to test. Could I really just have a bad O2 sensor and maybe that's what's causing my weird idle?

 

or clogged cat check your o2. If you plug in an OBD scanner, it should give you the readings of the o2 sensor.

 

a surging idle is indicative of a vacuum leak. Look for a hose that has come undone on the intake manifold.