Whenever its rainy or really wet outside, the engine loses almost all power. The best way I can describe it is like the engine is misfiring on several cylinders. However, the check engine light doesn't flash like it does when the engine actually is misfiring.

Sometimes, if I really mash the gas it will suddenly catch and run at full power until I slow back down again for a light or something, then it loses power again.

The car runs fine when its dry outside though, not even a stutter.

Its a 1998 Z28 with about 110k on it. The only mods are pacesetter headers, and those have been on for a couple years now with no problems.

Any ideas anyone has would be very helpful.

 

this is just throwing ideas out, but maybe your maf is close to failing, and the humidity causes it to malfunction noticeably? or maybe the same thing with your PCM.

 

might just need new wires or maybe a bad coil pack (wires are not a common problem with how short they are.)

Also, I had a problem with my 98 and the routing of the ground wire from the drivers side strut tower (if I recall correctly) that goes to the harness for the BCM. Finally after 2 trips to the dealer when it was under warranty, they found moisture was running down the ground and into the BCM (body control madule). after they fixed it, they repositioned the ground to be routed slightly different. that way water would run and drip off rather than straight into the computer.

I believe its the wire just below the white sticker and above the fuse block in this pic:

http://www.gmhightechperformance.com.../photo_32.html

 

My 95 Z used to do the same thing. Turned out that water was seeping in through the hood vents, dripping down onto the coil.
I could see a blue plasma like discharge looking straight down behind the coil between the block and the coil. It's tough to see, you really have to look at night and know exactly where the coil is. A new coil didnt fix it. The end of the center coil\plug wire was fried like charcoal and immediately broke of the coil connector. I just stripped it back to the good unburnt fiber and crimped on an old, (great brand though), do it yourself plug wire kit plug that fit into the coil.
Still runs like a scalded dog. And this happend about 9 years ago and @ 55000 miles with this quick fix. Water definately gets into the hood vents and soaks the engine hood insulation. Where it goes from there it's anyones guess. Water always wins.

 

sounds like coils or wires need checking. i had the same issue with some of my cars turned out to be bad coils.

 

plug wires

 

I had the same prob....check your spark plug wires, I had one that was cracked and every time it rained hard like clockwork it seemed like it ran on only a few cylinders because the wires were arching over.

 

sounds like a bad coil to me.