I have a problem with my S-type. About a month ago, while on the way back from a 200 or so mile round trip my engine check light flicked on. I panicked, stopped the car and called the AA. Much to my embarrassment, after waiting about 3 hours for help, the AA man fired up the engine, no warning light. He checked under the bonnet ect but could see no issues so off I went. About a week after that I noticed the idle had become rougher, and then a few days after that the warning light was back on. Its being going off and on sporadically ever since, and whenever I've plugged the Diagnostics machine in it comes up error free. Has anyone else had this? The cars got the 4L v8 engine, and is not high mileage. Any ideas?