I've used a whole can of carb cleaner and can't find anything. You're referring to the brake booster ya?

*UPDATE* So I replaced the PCV, installed a digital tach and set the curb idle to roughly 800 rpm, the truck ran great for the last 3 weeks or so and then today began to show the same symptoms. Most notably the idle while at a stop dropped down to around 500 and i had to feather the pedal to...

It doesn't seem to be caused by fuel level however the tank doesn't take fuel well. It tends to spit back if filled to quickly. I haven't checked the vent yet.

Ok I did find a vacuum leak on the manifold when I first purchased the truck. I capped it but will check closer. I didn't think about timing as its an intermittent problem but will pick up a light today. Thanks for the reply. I'll post my findings.

Hello, I've read thru these forums many many times to diagnose and repair my vehicles yet this is the first time I've posted. I've recently acquired a 1975 f250 custom and I'm having an issue with stalling on decel, or while braking, or while going downhill. Most times the idle is perfect and...