I have a 1991 oldsmobile 98 and have been driving it for years to work, about 3 years ago it would like miss(lack of a better word) out of the blue about 3 times and then be fine again for about 100 miles, then it started missing about 50 miles and now it down to about 15 miles. Runs great otherwise and starts easy you forget about it and then out of the blue it will do it again. A friend said it sounded like a fresh air sensor, but i could not find that listed on the car. idea's?