Another common engine tuning modification is a throttle spacer. This is a thick piece of aluminum you bolt between the throttle body and intake manifold. The additional space creates an increase in air velocity coming from the throttle body into the intake manifold. The spacers are also typically threaded along the inside, and this twists the air rushing into the intake manifold which creates more velocity.
This ultimately translates into a crisper throttle response on the low end which means from a stopped position the initial acceleration has a quicker response. This is especially helpful for Wranglers utilizing more low-end torque. The spacers typically rob some performance on the top end, but most Wranglers never excel in top-end performance anyway.
In addition, some throttle body spacer manufacturers claim there is also a slight improvement in gas mileage. Anywhere from 1-2 mpg. These estimates are debatable, especially since the increase in low end throttle response typically translates in a more aggressive start from a stop position which demands more fuel. Nonetheless, this an inexpensive modification with very little drawbacks, and it’s something that can be easily installed/removed if you don’t like the results.