My 86dl auto is getting unacceptable gas mileage. I can barely squeeze 230 miles out of a full tank. I thought I had definatly overcome the problem when I went to replace the intake manifold temperature sensor; upon doing so I found that the air intake line between the AMM and the intake manifold had cracks and was leaking in an uneven mixture of air. After I had it all apart I replaced the manifold temperature sensor anyway. In addition to the sensor and air line I checked the timing, replaced my o2 sensor and swapped out of my dads 89 wagon air mass meter. Before these replacements I was getting about 210 miles to a tank. I was expecting my car to leap from 210 to 280 or more miles, seeing as how my dads wagon gets more than 300 (even with my AMM)... but I was only able to achieve 20 more miles. I run 89 octane amoco fuel and castrol syntec blend. The car seems to have good power and doesnt smoke or burn oil. If I run 87 octane It seems I can get a few more miles but then I can hear marbles in the engine under load. If I run 93, or whatever hi-test is, I actually get even poorer mileage. My odometer is reading correctly as well, compared to mileage markers on the highway. Next on my list in spite of what little effect I beilieve they will have are a new cap and rotor, 8mm wires, NGK BP6ES plugs even though I installed champion platinums about 1500 miles ago, and maybe a new coil. Thoughts? Comments? Suggestions? Im open to pretty much anything at this point.