After it rains, either that day or the next,my car (91 Formula L98) will stutter and not rev above 2100 RPM's while in drive, and the whole car will start to shake. I can put the pedal to the floor and it will only slightly accelerate at about a mile an hour every few seconds, until I let of and ease back into the throttle. Nowtomorrow, if all goes according to schedule with no rain, it should be fine. Ok, so, I am supposed to look for possible areas where water is getting in under the hood into theengine compartment first right? Then am I to try and see if the ignition components are getting wet in the process? Any other ideas or suggestions here? Thanks in advance.

 

I had that exact same problem with a 71 Chevelle YEARS ago and every time it rained the car would stall or shake and sputter and in the end it turned out being a hairline crack in my distributor cap. I did a full tune up after I found out the cap was the culprit and didnt have any more problems until I sold it. I dont know if this is your problem or not but worth looking into...

 

I agree that it's most likely an ignition problem whether it's cap or wires with bad insulation. Check the ignition sytem carefully.

 

I agree, either cap or wires.

Consider a HyperTech coil/cap/rotor and a set of MSD 8.5mm SuperConductors.

 

yes, my parents had the same problem on their 68 I-6 Nova. Ignition related.