98 Volvo S70 stalls whenever it rains

My 1998 Volvo S70 Stalls at stops every time it rains. It very seldom does this if its not raining but does it every time it rains.

After driving it awhile it stops stalling. A gas additive that removes water helps but not after a heavy down poor.

Your Volvo requires a “tune up” every 30K miles. A tune up means new plugs, plug wires, and distributor cap/rotor. Most likely culprit is bad plug wires, followed by an old distributor cap in causing your symptoms. Change these items, and especially be sure you are using high quality plug wires. Your problem will disappear.

using high quality plug wires.

I agree, but don’t equate expensive as high quality. I suggest OEM brand parts. The original stuff is good. The fancy colored fat wires and such are, in my experience, cheap quality; fancy looks but poor performance and life.