Volvo: loss of power on a rainy day, volvo 740 gl, elements of the weather

Question
I own a 1989 volvo 740 gl with 190000 miles on it.  When it rains the car will loss power as if the distributor cap was cracked. I have replaced cap rotor plug wires fuel filterto no avail.  It appears to me that the caps front section is open to the elements of the weather I looked at other volvos and they all look the same.I was also wondering if it could be a vacuum leak that only acts up on rainy days Thank you  timothy lessard

Answer
Tim,
You say loss of power, now a problem in the secondary ignition system would be an engine miss. I would advise you to check fuel pressure when this is happening see if "loss of power" is due to low fuel pressure. Also when the MAF sensor goes bad the symtom is very much the same. Are you able to get any codes from your vehicle?