My girlfriend has an automatic '93 Volvo 850 GLT that shudders and stalls when it's wet; both when it's actually raining and even if it's just misty. The car always starts fine, even in heavy rain, but after driving a couple minutes it stalls.
It usually happens on her morning commute if it's damp out - it never stalls if the engine was already hot or the car was running before the rain started (even puddles don't present a problem then).
If she starts it in wet weather the idle is rough: no real peaks, but it'll dip below 500 before it catches itself. It doesn't stall during the idle - only after driving for a couple of minutes. The tach will bounce around, dipping and spiking up to 3000 for about half a minute before it stalls at a stop sign/light. On two occasions she's noticed it bouncing and pulled over before it had a chance to stall. After about 20 minutes of rough idling the car seemed to right itself and it ran smoothly again through the rain.
Last time it was wet she tried racing the engine (keeping it between
2-3000 for a minute after ignition until the engine was warm), but it still died a couple minutes after leaving the driveway.After it dies it won't start right away, regardless of how long you crank the engine. Engine starter does nothing. It takes about a half hour of just sitting there before it will start again. It always starts again though, even if it's still raining. After it's restarted it runs fine in the rain.
I suspected a cracked coil but I couldn't see any sparks when I looked under the hood last night. Today was nice and dry, so I started the car and tried spraying the engine compartment with water while it idled. I emptied the entire spray bottle onto the engine but no sparks. I even tried spraying the grille to see if water droplets were being sucked up the air intake, but it kept running smoothly. The idle finally got a little bit rough when the spray hit the area around the belts (passenger-side of the engine).
We took the car out to see if driving would cause it to stall and sure enough, it died at the first stop sign. I'm outta ideas, any suggestions?