I have an 82 F2 with the 300 straight six. The truck runs pretty good when driving but it almost dies when it idles. I was looking around and found a stray vacuum hose. It appears to becoming off of a connector with three other hoses that screws into the intake manifold. I had trouble locating it on the Vacuum diagram. At idle there is vacuum in the line and when I cover it with my finger the idle gets worse and almost dies. I'll post a picture so you guys can get more of an idea what I'm talking about.

 

The long hex nut that has the vacuum lines hooked to it is a vacuum tree. there may be another nipple on the bottom that is hard to see that the hose fits on. where does the other end connect?

 

I'm holding the end that is unconnected. The other end connects to the front of that vacuum tree. So the hose closest to the front of the engine bay

 

The long hex shaft is your main vacuum source.

 

Yeah so one end comes off the main vacuum source on the front port there and I'm not sure where it is supposed to connect to

 

It could be an intentional vacuum leak that some PO installed because he figured out the engine runs better like that... this is kind of common for people to do when they "remove the emissions crap" and/or "clean up the engine bay" to "make it run better."

 

I see. If I'm reading the vacuum diagram correct, the line goes to either the vcv or tvs

 

See if that loose hose is supposed to connect to the temperature sensor on top of the air cleaner.

 

I tried hooking it there but it seems to be kind of a stretch and makes it run a shade worse to about the same

 

Okay, that hose supplies vacuum to the temperature sensor located in the air cleaner housing. When the engine is cold, the sensor allows vacuum to be pulled through the second vacuum hose [two hoses attached to the sensor] to a servo motor located on the intake snorkel [where air enters the air cleaner]. This servo motor moves a door [flap] which then draws warm air from the exhaust manifold area. When the engine is warm, the temperature sensor blocks the vacuum and the door opens such that cool air enters the air cleaner through the rectangular flexible hose connecting the snorkel with the radiator support near the battery. In actual practice, this system moderates between cold and hot to maintain a desired temperature [~105F] inside the air cleaner. This prevents icing of the carburetor on cool damp mornings.


With the hose being loose [as shown] and open, there is a definite vacuum leak. This will be noticed most at idle and low speeds.


If this situation [loose hose shown in photos] is not recent, I suspect someone has adjusted the idle air/fuel mixture screw [at the base of the carburetor] to compensate for the vacuum leak caused by the vacuum hose being disconnected. Reconnect the hose or at least, plug it [a golf tee works well] and with the engine at operating temperature, adjust the idle air/fuel screw to the smoothest idle.

 

Alright I'll get that done. Thanks for the help. Glad to get this thing back running again

 

Off topic question. What's foamy coolant mean? I'm afraid to hear the answer but it's it foamy coolant in the radiator and the crankcase has some foam.

 

Update. Truck blew head gasket so the guy took it back and I bought a 79 with a 400 and C6. Runs really great