I just get one thing researched and my wife tells me there's another problem with her 1988 300sel. Seems it's beginning to surge when she's sitting at idle. The only thing I've done to it recently is new plugs and air filter. It runs smooth, but it surges from idle rpm to 3500-4000 rpm when it sits in park or neutral. She didn't notice it when it was in gear. Could I have a sensor that's going bad? Anything I should look for? Thanks in advance--Nick