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Discussion Starter · #1 ·
So, my car has a very light miss at idle, and during open loop operation it is a little stumbly when you hit the gas. It idles cold at 900 and warm at 900 or sometimes it will idle nicely at 750, and then again sometimes it will surge very systematically from 400-1300, but thats is pretty rare. I have been checking for vaccum leaks and such and have been replacing hoses too, but today I noticed that the throttle body and IAC mating surfaces are different. The IAC has two completely surrounded holes, whereas the throttle body has two but one is not surrounded completely. It almost looks like it was cast this way, but I didnt think that could be right... I attatched a pic, is this broken or normal? I looked but could find no pics of throttle bodies without the IAC plugged in. thanks
 

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Discussion Starter · #2 ·
just an update, I am getting 12-13 inHg of vaccum at 750 RPM and 15 at 1000 RPM. This seems to be significantly lower than what most people have. I sprayed carb cleaner everywhere, at all of the vaccum line connections, and manifold bolted surfaces and got no rise in idle...

2 things that worry me...

1) MAP does NOT hold vaccum (engine off) I think that it needs to hold vaccum right?

2) EGR does not seem to have any vaccum at all, but vaccum is getting to the tree before it. I have always gotten a code 34 running, and KOEO, but only after the engine has been run since last computer reset. Immediately after computer reset I get 11's. Is this why?

Also, I tested the vaccum at the manifold, but i couldnt get the 2 small hard lines capped off in the back of the manifold, I did test though at all spots on the maifold and got the same weak vaccum. I dont think that I have a leak in my manifolds, so what else could cause this type of problem? Is there any way I could just not be making enough vaccum?

Thanks guys
 

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That photo is out of focus. That vacuum measurement sounds a little low but nothing dangerous, although it may piss off your vacuum sensitive speed density computer.

You may want to check under the dash for any disconnected vacuum lines.
 

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nothing wrong with the casting on the tb,also you should only have vacumm at the egr when you accelarate(very little) not at idle.
 

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Discussion Starter · #5 ·
Why does the throttle body do that then? I mean not create the same full circle shape around the 2nd hole as the IAC? Also, do you guys have any ideas on why I might be not generating enough vaccum? I guess I could have a manifold leak, but I was very careful when i put on the Cobra intakes....hmmmm.... well I guess ill keep searching, thanks guys.

oh what about the MAP?
 

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I think they hold vacuum. I've got one here, off an '88 econoline, and it feels like it does. I'd think that the car would barely run with a ruptured(?) MAP. Is the housing cracked or anything?
 

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My BBK throttle body also has one hole that is a different shape.
 

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Discussion Starter · #8 ·
I will be checking my MAP sensor more thoroughly soon, but I have yet to find a crack. When you guys test your vaccum is it steady? Mine seems to be very unstable as the needle shakes extremely fast on the gauge, and kind of wanders between 12 and 14 inHg. Just curious what you guys are seeing, thanks
 

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Mine sits at about 14" at 900 rpm. It can wonder within an inch or two but not much more than that. I used to get about 16" steady with the stock cam.
 
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