Sick RPM when raining

When it's raining out, my RPMs are pathetic when in drive.

When in park it's fine, but in drive, it goes SO low, like 200-300...

Don't mind the odometer, it's fried, it says whatever it wants to. The pictures were taken around the same time.

In Drive:
http://img.photobucket.com/albums/v3...24-10_1701.jpg

In Park:
http://img.photobucket.com/albums/v3...24-10_1706.jpg

It's done this with 3 different Optis, different plugs and wires. All new set installed, STILL does it. New coil too, PCM, and ICM.

Bad tach or short in a tach wire theat's getting wet when it rains? Does it feel like the car is idling lower when it's wet out?

Yes, it does idle lower, it's not a tach failure. If I datalog from the computer, it is SPOT on.

When raining, in drive, tach shows super low idle. I let go of brake, a snail would surpass me idling forward.

IAC motor or tps sensor possibly?