Will high humidity affect idle speed on starting?At cold start the engine will rev at 2000 rpm or so.Sometimes it will drop to normal soon after.At other times the vehicle will surge at red lights when brakes are applied.Does not happen all the time but seems to occur with high humidity,above 65-75%.Thoughts?

SOURCE: My idle is all over the place!

Have you tried cleaning out the throttle body and injectors with a cleaner?

SOURCE: high rev after cold start

I would agree.

SOURCE: When started idels high about 2000 rpm then drops when hot cold ?

the iac probably has carbon built up around it this controls the idle speed try cleaning it first,if not it could be a bad iac or a vaccum leak that the iac takes some time to compensate for to control idle.

SOURCE: 1996 Jeep Grand Cherokee will not start or idle

Two0 items to check...manifold air temp sender, coolant sensor and idle air control valve (may need cleaning. OK that's three...I lied.
Good luck!

SOURCE: I have a 2000 Jeep Grand Cherokee, 4.7litre V8.

code P0320 no crankshaft reference at PCM.......most likey both problems are related sounds like you need to replace the crankshaft sensor, it is located on the right side of engine block, just above the starter motor, we see a lot of these fail. if you let it go to long you might get to take long walk, i will tell you what my farther used to tell me, if you don't want to fix it then don't drive it no farther then you want to walk.

let me know if there is any thing else i can do for you.