I recently bought a 1994 3.8L V6 Mustang with an auto trans. I got a pretty good deal ($900) on it but I don’t know much about the history of this car. I do know that the engine has been rebuilt and has had some modifications.

I was told that it has had a mild cam installed, non-stock headers, some sort of electronic stall speed in the trans(???), and an upgraded fuel system (adjustable fuel pressure regulator, fuel pump, 19lb injectors). I have swapped out the 19lb injectors for the stock 14lb injectors because it was running really rich. I think it has improved the way it runs.

The problem that I’m having is when I start the car (either in park or neutral) it revs up to around 2800 rpm’s then idles down to 2100 rpm’s. When I put it in drive or reverse it drops the idle down to 1100 rpm’s. The engine runs extremely smooth and sounds great.

I have tried adjusting the fuel pressure down but that hasn’t changed the idle to much. I’ve adjusted the idle set screw all the way out. The throttle cable does have a little slack so that’s not the issue.

I’m thinking its something with a vacuum leak but still not really sure. I only just started trouble shooting this car. I hope I can figure it out and any help you can provide with be much appreciated.

Thanks.