I've been putting in a bottle of chem tool when I fill up and I'm not sure if it is just a placebo affect, but for a couple of weeks my 90 240 just seem to be purring along better than ever, plenty of power on the highway and in city traffic at the traffic lights. And now I'm back to that sluggish feeling and what seems to be poor MPG(odometer broken)When it runs well, It's almost like something has kicked in and the brick rides so much better and seems to rev a bit higher and smoother. Is there something I'm missing as far as tune up or sensor operation/malfunction