I have just purchased an 86 F250 with a 302, from an auction.

It had a bad vacuum booster and needed an Ign key cylinder.

The booster was hissing inside, and when you hit the break pedal the idle would drop and sometimes stall.

OK I replaced the booster and the key switch. It still stalls.

Let me give more info on the stalling.

Hot or cold, sometimes when you come to a stop at a light, only sometimes, but more often than not, it will load up on fuel stumble and stall. When stopping the idle seems to fall first then it will load up.

It will usually re-start on the first try, and run smooth and fine, for a stop or 2 then do it again.

Also if you stop at a store or something and shut it off, when you try to re start, sometimes its like no spark at all, it just cranks.
If you turn the key to off then on the fuel pump runs a second then you crank and nothing for two or three more trys. If you wait about 30 seconds after this it will start and idle fine, until the next time you stop at a light or shut it off.

To me it acts like something is telling the injecters to open and add more fuel but only sometimes.

I have raised the idle a bit to help it. If you use the gas and brake and keep the idle up it dosent happen. Only if you let that idle drop, too low it seems to try to compensate by adding fuel, then dies.

Any ideas would help.

 

Hi, the stalling could be the TPS sensor (throttle position sensor) John

 

i would clean the throttle body and more importantly the air bypass valve which actually controls the air your motor gets when its at idle it usually gets carboned up and cause the idle woes you describe take the valve off the throtle body and clean it up with some carb cleaner, also could be the map sensor and or fuel pressure regulator, i would try the latter b4 the map sensor