Picked up a 98 Neon for a song because the owner thought the 95 engine that he had put in was frozen and did not want to mess with it anymore. Turned out it was just the bolts he used for the flex-plate were too long and binding on the bearing journal. My problem is that I have never been able to get the engine to run smoothly especially at idle. It surges a little after it warms up. I've done all the basic tune up stuff which helped a little. The only code I get is a bad O2 sensor and that is just recently. All electrical connections to the engine were verified. Is the 98 PCM compatible with the 95 engine or do I need to look elsewhere (like the EGR valve)?