99 hyundai accent check engine light comes on after rain

I have a 99 hyundai accent GL 4door automatic transmission...whenever we get a steady rain or hard rain for a day or more the next time i use my car the check engine light comes on shortly after i will be
driving down the road..at first it will flash just a few times and then will stay steady...it might be like this for several days depending on the weather or how much i drive the vehicle but i know it won’t go out until something is completely dry it seems..maybe a couple of dry weather days etc...then it might not come on for weeks or months..the car has 136000 miles and i have owned it since july 04 when it had about 65000 miles..i have put a new timing belt a few miles after i bought it..the car for the most part runs good except when this happens..even though it has been doing this for several years now i have never taken it to a garage because either i did not want to pay a garages diagnostic fee or when i wanted to stop in the check engine light was not on...now its spring time and we usually get alot of rain and would finally like to find out why this light comes on and why it sputters at first when the check engine light is flashing....does anyone know how to get the codes and what they actually mean?i have read on some of these sites people say places like autozone or advance autoparts will do a free test for the check engine light...is that true?i hope i can get some feedback on here.
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cleo0399 wrote:

You did not say where in the world you are but did mention Autozone. The Autozone near me will check for free if not too busy. Advance I have never heard of.
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Head to the auto store. Yes, many will do it free in the hopes of selling you parts. Even if the light goes out, the computer will retain the codes for a time after.
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On 5/14/2012 12:42 AM, cleo0399 wrote:

A flashing check engine light indicates a real-time misfire. Since it happens only in damp weather it's most likely due to an ignition-related problem, either spark plug wires (if your car has them, some are coil-on-plug) or ignition coils. Autozone does do free scans, make sure you get the actual Pxxxx code so you can look it up. If your car does have plug wires and they have never been replaced, it is very likely they are shot. One way to check them is to watch the engine running at night, if they are really bad you may see arcing. You can also try spraying a little water on them from a spray bottle and see what happens.
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