I just bought a 1994 STS. 95,000 miles. I was having a problem with the engine surging when idling,so I brought it to a Cadillac shop and found I needed to replace the PCM. OK that's done. Are there any problems that typically follow replacing the PCM? This is my first Cadillac but have found in the past that one problem usually proceeds others. Anything I should be watching for?