I have an 88 formula with a 305 tbi recently rebuilt 2000 miles......... I have been tracking my gas mileage and noticed That I am getting 13miles per gallon. Used to get anywhere from 16-17 to 20-21 mpg. The 16-17 was when I had a bad map sensor. This is the worst I have ever had. I just put a new O2 sensor in. Me and my friend were playing with the tbi tonight because in drive I was idling at 1000 rpm now its at 500 which is a little low. But after reading the tech article I know how to set it. How ever when I hooked a computer up to the ecm up to it told me that at idle the map was reading 7ihq??? whic I am not sure on what this means. Is this a low vacuum reading because at idle my engine pull 21 pounds of vacuum...... well any way any help would be appreciated...... tonight I checked and i got 11 mpg which is un acceptable

any help would be appreciated
Kenny