The other day my GLi started to act as though it was misfiring, jumping idle, lagging acceleration, hard starting. I did all the checks that came to mind. Plugs, Distributor cap and rotor. To no avail. I checked the air filter, grounds, and cleaned the throttle body. I even went as far as putting the battery tender on for a few hours to make sure it was good and charged. Lo and behold, the one thing that didn't cross my mind though it should have been the first. A crack in the intake tube just after the air box underneath. not sure how it got there probably an overtightened clamp about a pencil size. easily patched with my favorite repair item in the world, duct tape. To find it? Start the car, open the hood, take a can of carb cleaner, and spray in small spurts around the intake parts you think are leaking. if the engine revs with the spray you've found it. and you didn't even need to bust out the wrenches.