My '89 Marquis has a miss at cruising speed. When the "economy" readout on the dash gets up to 23 mpg or so, the engine develops a misfire. Every second or two, it jerks. Give it just a tiny bit more throttle, so the readout drops to 22 and the engine is pulling ever so slightly, and the miss disappears. I figure it must be a dirty injector? A spark plug or wire should miss more with more throttle. No engine lights come on. The car sat for a year or so and the gas went bad, I put some Wynn's injector cleaner in it (and fresh gas) but haven't run it far yet. What do you guys think?