Fast idle, In search of air leaks |
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Fast idle, In search of air leaks |
Rand |
Jan 25 2006, 05:54 PM
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#1
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Cross Member Group: Members Posts: 7,409 Joined: 8-February 05 From: OR Member No.: 3,573 Region Association: None |
Been trying to nail the fast idle problem for a while. Have absolutely ruled out any vacuum leaks above the throttle body. Have replaced the injector seals. That leaves me with.... Leaking around the butterfly in the throttle body? Or somewhere else in the plenum or intake runner seals?
If I put my palm over the air intake, it does choke it down. That makes me wonder if air is getting around the butterfly (since the idle air adjustment screw is all the way closed). But I'm a noob on this detail... Please comment on this!! I would think a crack in the plenum / air distribution box (whatever you wanna call the air box under the throttle body on a '75 2.0 Djet) would be rare. But I'm down to checking rare things on my list. I guess I don't mind taking all that apart because I haven't been there yet and wouldn't mind painting the plenum and air intake tubes anyway. Sooo.... Anyone have photos of disassembled plenum, intake runners, etc.? What will I need if I take this apart? (Seals/gaskets? Anything else?) |
lapuwali |
Jan 25 2006, 06:45 PM
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#2
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Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743 |
If you can't kill it with your hand completely covering the throttle body opening, then you still have a leak somewhere. The only places air *should* go around the throttle plate are the AAR, the crankcase breather hose, and the idle air screw. The idle air screw still gets it's air from just above the throttle, so the hand trick should close that off, too. If you've sealed off the rest, then the air has to be coming from somewhere other than the throttle opening, so the throttle plate is not a factor. The throttle could be wide open and the engine should still die if you close off the TB with your hand.
I've no idea if cracked plenums are common (though I'd suspect a split seam would be more likely). The runner connector tubes are commonly bad, so replacing those would be a good idea. The head to runner gaskets would be at the bottom of my list, but if you're pulling the runners, anyway... The MPS hose is the only other thing, but a serious leak here would also make it run like crap 100% of the time. |
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