the car starts up just fine, and seems to only do it while warmed up, and is fine when its dry. my k&n is fairly clean, and i haven't cut the plastic underneath, so its not sucking a bunch of water. two weeks ago i changed my opti, and plug wires and has been running great since then. yesterday it rained and it would idle really low, obviously missing, and had a bad stumble, but would clear up all of a sudden and just take off. it seems to be related to throttle position instead of rpm except for the weird idle. today it didn't rain as hard, and it ran good most of the time, but i could feel a stumble a few times. the car has 161k miles, and here's what & when i've changed:

opti-2 weeks ago
plug wires-2 weeks ago
plugs-20k miles ago (pulled 2 when i did the opti, & looked new)
o2's- maybe 30k miles (gm parts)
coolant temp for pcm-20k miles (gm part)
1le intake elbow-30k miles
coil-2 years ago, maybe 50k miles

i'm going to get a new map sensor, iat sensor, tps, change plugs, clean the throttle body and maf, check my opti connection for corrosion, check for leaks after the maf, and ad a body ground. anything else i should do/check?

 

Check your waterpump for leaks, you don't want it leaking on the new opti.

 

There is a wire that runs near your AC clutch pulley, it leads to the starter.. Mine was doing the same thing, then it got worse.. If you wanna read my post do a search for Brick Wall.. Check that line though, it runs from the terminals up top to the AC clutch on the bottom, runs past that near the motor mounts then to the starter..Let me know what you find!