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Today I noticed a few things about my S13. First of all, behind the gas pedal there's a plastic stopper held in by one screw against a metal bracket. If you unscrew this screw and put the plastic piece aside, you'll notice you can get the pedal down a slight bit more.

Also, pop the hood and look at the throttle body. There should be 2 throttle cables running into it (they're steel cables like a bycicle's breaks would have). Push your finger down on them and check for any slack. If there's slack, you probably have pedal free play and lag, and ultimitely can't open up the throttle body all the way. This is simple to fix.

Notice the bracket the cable runs through. There's a threaded shaft that the cable is inside of and two nuts. Move the one closest to the throttle body closer to the throttle body until when that nut is pulled back against the bracket the throttle is fully taut. Now, to hold it in place, move the nut closest to the pedal down the shaft until it's tight up against the bracket. There should be no more slack on the cable.

In my 1990, I had to run the nut that was on the throttle body end all the way down the shaft to get it taut, but your mileage may vary.

I took my standard test drive route after doing this and I noticed a fair amount of improvement. My throttle immediately responded whereas before there was a tiny amount of pedal lag. It also seemed to want to rev a slight bit quicker.