I have been driving my 83 T/A since I completed my 92 305 TPI swap into it, and I have a few problems that I think may or may not be related. First, I am getting really bad gas mileage, 13mpg as calculated on my last tank. Second, it pops out the exhaust really loudly when in gear but coasting down a hill. Third, When driving and I take it out of gear, put it in neutral and coast, the RPM's drop really low (like to the point of steering getting stiff) and then it usually catches itself and returns to a normal idle. Twice it has actually died while doing this.

Here is my setup- stock 305 TPI out of a 92 T/A auto with the following exceptions: K&N air cleaner directly on the throttle body, Hedman hedders and y-pipe, Flowmaster exhaust, and a Fuel Injection Connection wiring harness. The chip is stock 305 auto programming but without VATS. The car does have a T-5 though.
My first thought was an exhaust leak, and I found one on the connection on part of the Y-pipe, which I welded up. I also replaced the oxygen sensor, but it still does it (I think maybe not as much, but hard to tell). Anyone have any ideas on this? I would be most appreciative. Sorry this is so long, but I wanted to give all relevant information.
Thanks,
Ryan

 

You need a T-5 prom. The IAC recovery when coasting is different between the Auto trans and the T-5. That's where I'd start.

 

I will try that, but do you think it will run ok? My understanding is that the manual and automatic motors had different cams (resulting in the 30hp or so difference). Would the programming be all wrong or would the computer compensate for much of the difference in closed loop? Thanks for the input, I appreciate it!
Ryan