1984 F250, what is this under hood plug? Rough Idle issue.

[ArdWrknTrk]

Ah!
So it's meant to 'un-flood' an engine that's had fuel boiling into the intake!

That makes more sense.

[Chad9]

I have one of these valves on my 460 also and have not messed w/it yet. Does anyone know how it should be turned? Wondering since I am having some hot start and idle after hot start issues.....

[Starliner]

.  .  .  And that is my main concern with those. If I dont know exactly how it is expected to perform, 36 years later how can I spec it? Bypassed.  But I see the logic in keeping it.

[ArdWrknTrk]

It either works, or it doesn't.

Blow or suck through the center.
Which side is connected?

Hit it with a heat gun (because boiling water is below the set temp)
Don't cook the plastic.


It's a simple wax pellet that expands (just like the water temp sender) they don't go 'bad' very often.

[vjsimone]

ArdWrknTrk wrote

So this is something that causes a bigger vacuum leak than the PCV itself?

Isn't the TVS in the distributor advance line a better solution to the issue?

My 360ci Jeep engines had the TVSs in the distributor vacuum circuit to advance the timing for an increased idle.

[Starliner]

Hmmm, I bypassed it but maybe doing so accounts for me having to feather the pedal for a little less than I minute before she idles on her own.
I know my idle is set too low but I am going to revisit that for sure.
I found a tach thanks to this forum.
Just swapped it in today.





Thanks a bunch.

[ArdWrknTrk]

The thermal valve shouldn't affect anything until it is overheating already.
But not having the vacuum restriction is going to cause the advance can to react too quickly to manifold vacuum.

Having to feather the pedal until the truck will stay running makes me think the fast idle cam is not set right.
Now that you have a tach, you have a better idea.
1,100 RPM is about where you'll be on a cold morning (highest step of the cam)

Tach looks great, BTW!

[Starliner]

I think you are right about the high idle cam, I will check it. I had it mostly set up but didnt have a vac guage to finish off with idle mix screws. I did the proper set up, then a friend got under the hood and started screwing with it "by ear".
If you want something done right .  .  .  

[ArdWrknTrk]

You need a new set of "friends" before your truck ends up irreparable.