This is an easy mod for most cars. I have been trying to think of stuff I have not done to my car and one thing I came up with was a spacer to put under the TBI. Of course nobody makes anything for a Metro and even if they did it is not worth spending much money on something so easy to make. Spacers can show a couple of mpg improvement on an engine using a carb or TBI injection. On multiport it can be hit or miss whether it works.
So you need two things to make one. A plastic cutting board and a TBI base gasket. I got my cutting board from RiteAid locally, it was a nearby store and it was exactly 1/2 inch thick. It cost 10 bucks.
Start by laying the gasket on the cutting board and drawing out the pattern on the board. Drill holes in the mounting bolt holes and some starter holes in the other areas. Use a dremel or a grinder with a deburring bit so it doesn't clog up. I couldn't find my dremel so I used an air grinder with a deburring bit.
One thing to note. You don't have to cut all the holes out. Some of them are much larger than are actually needed. They are used for vacuum passages and as long as they are big enough to let the vacuum source through they don't need a huge hole. On the main bore I made sure it was nice and smooth and properly sized to the manifold. The other holes I just shaved the plastic down so the vacuum signal could get through but otherwise didn't bother cutting it totally out. You can cut them out but it makes it take way longer and you don't gain anything.
Typical reports are a much better bottom end response and slightly improved mileage. I will find out soon with mine and report back. If I feel like it, I will make a second one and stack them for a one inch spacer. I am not sure what would work best on this setup one inch or a half inch. I might try both ways if I get time and if my mpguino ever comes in.