So I have a 1978 E-150 4.9L Six Cylinder, manual. Recently it started having a stalling issue which only happens when it is in neutral. When it first started it was difficult to start at times so my first thought was the carburetor and choke (Even tho it is only a year and a half old). I took it apart for inspection and everything looked clean and in order, cleaned up anything I could and got the choke and carb adjustments in good working order. The problem remained. I realized that the rough idle before stalling was encouraged by braking. This made me think vacuum so I checked all the lines, disconnected the booster and ruled that out. Most recently I've now noticed that when parked in my driveway on an incline the idle is higher. This has lead me to the believe that the braking and any downhill angle are a cause of the opposite. Braking while already stopped doesn't have an affect.

Anyway I am now stumped as to what to look into next. The fuel pump, like the carb, is only a year and a half old and appears to be working fine, fuel filter isn't clogged. And I don't know where else to look for vaccum problems. Any suggestions on where to go next would be greatly appreciated. Thanks!

 

This is easy to do and doesn't cost a lot! If you don't have one , buy a can of carb and choke cleaner then when the engine is idling, spray around the intake manifold where each runner connects to the head and also where it is connected to the exhaust portion of the manifold. They had issues in that area and that may save you some time and help to pin down a hidden vacuum leak.