can a bad break booster do this to the idle

Do what to the idle? If a vacuum booster has a leak, it will make the engine idle fast or rough. If the leak is really bad the engine might not idle at all.

The idle is crappy but if I where to pull the vac line off the booster the idle returns to normal

And that goes with any vac line I unplug it all does the same thing

It is a lot easier to carry on a conversation if you stick to your original post. Creating a vacuum leak is NOT the way to fix the idle.

I'm sorry I'm new to this still figuring this out

Have you done a tuneup lately? And if your truck has a carburetor, have you tried to adjust the idle speed? Checked your air cleaner filter to see if it is really dirty?

Yes I did a complete tune up every thing is new this vacume problem e is my biggest concern

Like I said it is not a vacuum problem. There is no such thing as too much vacuum. Vacuum is created by the engine sucking in air and is normal.

But how can it go from a real crappy idle to a good idle by pulling a vacume line that is strange

Not all that strange. Does your truck have a carburetor? Have you checked the ignition timing?

Good question... I have been watching but keeping my nose out but what YEAR?

Hey Ford! Maybe you can help this guy. If the truck has a carburetor I would be considering installing a new one.

What I gather is when you disconnect any vacuum line it idles better. That tells me clogged air filter, it's only getting intake air from a vacuum line and not through carb or TB

Previous post said 1987 and he says that it does not have an IAC so I am assuming it must have a carb but around that year most engines went to injection.

G'Day FoR. Does that make sense to you? That the air flow is increased by pulling the big hose off brake booster and allowing air IN?

If it has a carb and the choke is stuck to the on or closed position then disconnecting a vacuum hose lets more air in resulting in a better idle. Clogged air filter, same thing.

Reddraggon needs to give us some feedback. At this point we are guessing. I suggested the air filter but got no feedback on that so I don't know. If it had a carb, the first thing I would try is spraying some carb cleaner down it.

Ford - vacuum leaks on older cars will typically increase idle speed so that is not surprising. The cause of the low idle is what I am wondering about.

Now what engine? Last year of carb for 302 -5.0 was 1985, the last carburetor on a 351 is 1897. So there is a 'gray area' here

Thank You Bob... good help and good afternoon to ya

1987 not 1897. Slap myself

Um, reddraggon, you here?

It may have a feedback carb on it.

Crappy idle usually means the air idle mixture screws need to be adjusted out until the highest rpm obtained, turning the idle screw down to proper rpm when doing this, then a 1/4 turn out from that point. Factory had these either sealed, or a plastic lock cap on them. We always either knocked out the metal caps or pried off the plastic caps to get at them. If the choke was stuck closed, it would be trying to idle fast since it would be up on the fast idle cam, and would be choking out like an asthma attack. Timing will make it idle slow also if it is off. Pulling a vacuum line and it idling better tells me the idle mixture screws need to be adjusted.