I have a 92 Bonneville SE with 127,000 on it. Over the past several months, the idle has gotten rough. It seems ok until the car warms ups, then it gets worse. You can feel it run a little rough while driving down the road, but not real bad. I checked the codes and it showed a 13 and 31. So I put in a set of plugs, oxygen sensor, air filter. As well as a Alternator that started to be a problem. I have seen a small improvement, but still a problem. A year prior I put plug wires and a coil in it. 6 months prior to that I put a crank sensor and a ECM in it. Any help would be appreciated. Thanks.