1999 Buick Century • 90,000 miles

I have an issue with a car I'm working on. It seems to run fine, until it starts raining. Then, it starts sputtering and has almost no power to it. The oil looks fine, besides being low. The spark plugs look like they need replaced. The belt is squealing bad, needs replaced. Checked it with a code scanner and it gave me two codes; Engine misfire cylinder 1, and bad EGR valve. It is also losing coolant somewhere, and I can't find where. I haven't checked cylinder 1 spark plug, wire, or compression due to the fact it will be a job just to get to it and it's not my car. Can anyone help. I can't find any information anywhere, even on AllData? Am I safe it say it just needs new plugs and wires, or could coolant be getting in there and causing the misfire; even though it only happens when it's raining? FYI, how hard it's raining does not matter.
December 14, 2012.

What is the exact codes numbers you have not code descriptions?

Dec 14, 2012.
If this model is like a 1998, It may be that the fuel pump connector located behind the rear passenger wheel well may be getting wet. Check the connection by sliding under the car where the muffler is as look for a connector mounted to the inside of the body. This plug/connector has no clip to hold it in place and may be loose causing intermittent problems especially when it rains and water comes into contact with it.

Jun 1, 2014.