Idle Air Screw

[AB]

My Idle Air Screw has no effect.  Air still passes when closed all the way down with spring.  Could it have been damaged by being screwed to far into the body of the valve if so is there a fix?

[Benz Dr.]

Not that likely and more likely a vacuum leak or stuck warm up regulator. I would also check to see if your throttle valve is closed fully. Any one of these things, or a combination, would give you no response when turning in your idle air screw.

[AB]

Thanks very much for the reply.
I checked both of those items and they seem ok.
 
I put my finger over the idle screw hose and restricted the air flow with my finger and was able to choke the engine that way, hence my suspicion of the screw valve itself.

Should the valve close to zero flow?

[ja17]

The air screw will not completely shut down the idle air. Make sure the engine linkages are correct. If the venturi is not set right, you may be drawing too much air into the intake.

[stickandrudderman]

This is where a smoke machine becomes very useful.
You need to track down the source of air that is allowing the engine to run at the elevated speed.
Could be:
Throttle butterfly maladjusted.
Inlet manifold gasket leak (or some other manifold leak)
Aux air slide stuck open or pipe work compromised.
Brake servo hose split (or indeed servo itself failed)
Also check for incorrect ignition timing.

[mrfatboy]

Did I hear someone say "smoke machine"? 😜


https://www.sl113.org/forums/index.php?topic=27775.0

[AB]

Thanks much, 

I think I have a brake booster problem as the engine speeds up when the brake is pushed.
Again thanks for the list to pursue.  I will chase down the brake booster issue first as it seems the most likely.

I occasionally vape.  Is that enough smoke?

[Pawel66]

The revs will increase slightly for a moment when you press the brake - it is normal. Just a bit and for a moment. If it is a constant increase of revs - that is another story.

[Mike K]

To elaborate on Pawel's comment, press and hold the brake pedal, don't pump it.
You should see a slight rise and fall of maybe 50 rpm or less, which is normal as the chamber equalizes.
If the rpm rise does not return to normal after a few seconds, then there is a problem.

It could be the O ring seal between the brake booster and the brake cylinder, or could be that the booster itself is faulty.

Best,
Mike

[Tyler S]

Adjusting The idle air screw should only be adjusted/ will only have a noticable effect if the engine is completely warmed up. If backing it out causes the engine to race more than 100 rpm, the injection is rich. If it stumbles, its lean. The engine should not rise or fall ~ 100 rpm.