Complete, total, absolute, 100% waste of money. No rumor, no kidding. A spacer can do wonders under a carburetor and it can do wonders under the old no longer used throttle body injection type of throttle body.
But on the TJ's 4.0L where nothing but air passes through the throttle body, a spacer under the throttle body will do nothing. Some gimmick spacers even claim to swirl the air but by the time it gets past the valves into the combustion chamber where it finally meets up with the fuel, does anyone really think it'd still be swirling?
It's a complete waste of money. Yes I had one given to me.... no effect on performance, no effect on mpg. Only if you're suceptible to the placebo effect would you think it did anything.
All the above, of course, is just my personal opinion.
