i have a 92 240sx dohc. its got about 130000 miles on it. nothing major, electric fan, injen intake. i am having an issue with the idle. the idle when im at stop lights usually drops to 400 rpms and goes up and down sometimes but usually sits at 400ish. idle goes up and down a hundred rpms. but it doesnt always run rough, sometimes smooth. feels like it might be miss firing. not sure. but like i said it doenst do it all the time. Spark plugs are a couple months old. the tips of the spark plugs are a chalky white color. when it is running completely smooth it idles around 600 or 700 rpms. im in the process of getting a new tps.