Chasing an elusive air leak, idle screw all the way in..

[gintaras]

I don't know what else to do.. I have been chasing an air leak ever since I bought this bus almost 2 years ago.. I have driven 25k miles in 20 months, so it is manageable, but it sure would be nice to have her idle down at a stoplight..

I swapped out the air intake boot about a year ago, and that made a huge difference, but I have always had to have the idle screw turned all the way in, always idles around 1050 when fully warmed up, and sometimes, after a interstate speed jaunt, it just won't idle down, and I have to keep feathering the clutch to slow her down at a light, or turn off the engine altogether, this usually results in a rough few seconds after restarting, because of the rich condition.

So, I changed the intake plenum boots and gaskets last night, seems to idle lower, but still around 1000, spec is 800-950, but my screw is all the way down, there won't be any 900 rpm idling here.. I even tried to rub a little oil on the idle screw O-ring, no change..

So what is my next step? The throttle body gasket? That's about the only thing that I HAVEN'T changed.. I do notice a slight hissing coming from the brake booster line, but it is minimal, I was going to try sealing that joint with some Permatex High Tack gasket sealant, the same stuff I just used on the intake gaskets and also as lube to slide on the intake tubes.
_________________
1979 Deluxe Westy in Mexico Beige

[BayCreamPuff]

Definitely check the throttle body gasket. It's got to be a pretty big leak for the idle screw to need to be turned all the way in. Have you tried a smoke tester yet? It'd be cheaper than all this guessing.

Here's one for $79 - http://m.ebay.com/itm/281805683189
_________________
Cream Puff
'79 CA Stock FI Deluxe Campmobile

Earl Grey
'87 GoWesty 2.2 Westfalia

Marsha Mellow
'00 Eurovan VR6 Full Camper

[williamM]

smoker, or metered down air pressure to 5/6 # and blown onto a vacuum port then attack wiith windex look for bubbles.
_________________
some days I get up and just sit and think. Some days I just sit.

opinion untempered by fact is ignorance.

Don't step in any!

[Randy in Maine]

If you were to put some duct tape over the "power brake booster T" at the air plenum, does the high idle speed go away?

Are you sure your centrifical advance function of the distributor is retarding as it should?

[mikedjames]

If it is hissing suspect it.

There should not be air flow through a brake booster hose apart when the brakes are applied, and that for a short while until the vacuum builds up in the servo.

Expect any fabric covered hoses to be hiding cracked rubber.

Poke around with a length of hose to your ear when the engine is running and listen for a harsh hissing noise from any vacuum leaks.
_________________
Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[SGKent]

possibilities and common would be

brake booster leaking
EGR diaphragm perforated
injector seals
Any damage or rot in the Tee that the brake booster comes off of
bad line coming off Aux air valve
throttle body to plenum seal
leaky FPR diaphragm or decal diaphragm

You can test at each spot except the booster with a little Berryman's B12 spray. Don't soak it, just a little spray will cause the idle to change. If you haven't changed the injector seals that is something you have to do at least every 10 years / 50,000 miles or so.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[gintaras]

[gintaras]