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Discussion Starter · #1 ·
I have a 91 with a 2.05 and for quite some time I have been having a problem with my idle bouncing up and down. I tried replacing the IACV and the Fast Idle Valve with no luck. Finally after being tired of spending money on replacing parts that didn't need to be replaced I took the car to the dealer and had them find the problem. Turns out that I have a major leak at the gasket between the intake manifold and the head. I decided to try the job myself seeing the dealer wanted over $400 for the job. I was wondering if anyone has any tips on doing this job. I don't have a manual and seeing that I want to do it this weekend I don't think I can get one that fast so any help is really appreciated. Either way I will post the outcome of my project seeing that the archives are full of people having a similar problem.

Thanks

Matt
 

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taking just the intake manifold off our cars is a bit of a pain. The nuts that hold it on are hard to get a socket or wrench on, even when the head is out of the car. (at least mine were).
If you have some good tools and a good jack, you should be able to do it alright though.

I really just have one piece of advice: when you take the manifold off, make sure you get ALL (i repeat ALL) of the gasket off. It's probably baked on there real good, but if you leave some little bit on there you'll probably just wind up with the leak again.

otherwise just find a good manual and follow it. You should be able to do it with some elbow grease.
 

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Discussion Starter · #4 ·
Thanks for replying, The diagram was a great help in seeing what I was getting into. I have got the almost all of the old gasket off and should be ready to finish the job as soon Sunday.
 

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Discussion Starter · #5 ·
Problem solved. I was able to get the job done this weekend and now the idle is perfect. Thanks for the help
 

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speaking of the butterflies.... I have an IM w/ the butterflies... I don't want the hassle of taking my b21 IM off of my b20a in the car now... can i just remove the butterflies, have the IM extrude honed, and then port matched to my b21 head and not lose much?
 

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it's easier and cheaper just to swap the intake manifolds. It doesn't take long...

If you're swapping in a b20, i'd keep the b20 intake and find a way to make those butterflies functional. They provide a healthy dose of low-end torque over the B21 intake manifold.

The b21 had enough torque to compensate for the difference, so honda went ahead and designed the IM for high engine speed flow. Since the b20 doesn't have that extra bit of torque, the secondary runners help bring it back -- IF you can make the butterflies work...
 

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it's an ecu reprogram/swap.... that's why i didn't do it the first time.... i'll end up having to do this in two or three steps now probably.... although I still ponder the fact that I think the 5th gens have butterflies right? what about itrs?
 

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you don't have to do an ECU reprogram or swap to make the butterflies work...

they're vacuum controlled. You could go about it a couple ways. Since i know a good bit about electronics, i would just make my own little device to open it. Tap the upper blue wire on the ignition coil and have the device monitor engine speed. based on engine speed, the device would activate a relay or a valve that would open the vacuum line to the butterfly plate.

without vacuum, the butterlies are always open. when vacuum is applied, the butterflies close. at a desired engine speed, vacuum is release and the butterflies slam open.

shoot, since you would be making your own control module, you could have it vary how much the butterflies open if you wanted. It's all a matter of how much time you want to put into it...
 

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hell, if you want, i could design one and sell it to you...

i wonder if there's a market in producing "external butterfly controls for 90-91 preludes using the b20 intake with secondary runners"

interesting...
 

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Isn't the GSR / ITR setup, heck, even the 5th Gen IM: don't they all have a butterfly setup?

I would be happy to talk about your design... Have a guestimate? Jump seems excited too! Are you thinkin' what I am thinkin'? more down low for street/autocross/rally?
 

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mouchin what the hell are you saying exactly? butterflies are open on idle and then close as the revs go up? or the other way around? i thought they opened up in 88-89 ludes at 4500 rpm to provide more air for the higher rpm. u confused me now..
 

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your right. The butterflies close off the secondaries untill they're needed to flow more air (whatever that rpm might be).
If you want a simpler way to control when they open, you could use the "home-made boost controller" idea.
Just get two male threaded barb fittings, a female coupler, a spring from a ball point pen, and a small bearing. put it all together with the spring pushing the ball bearing against one of the openings on the inside. Then you tighten or loosen to adjust how much pressure it takes to open (or push the ball bearing back). I've seen this used before as a cheap boost controller alternative.
You obviousely would have nearly as much control as mouchyn's idea, but it might work.
 

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actually, the butterflies are ECU controlled. It's only the actual movement of the butterflies that is controlled by vacuum. The ECU sends a signal to a valve, which allows vacuum to go to the vacuum solenoid, and it closes the butterflies. When the computer sees a certain rpm, it stops sending the signal to the valve, and a spring pushes it closed, which stops vacuum from going to the solenoid, so it opens.

You *could* make a controller for the butterflies, but it couldn't be vacuum controlled, unless it was fairly complicated.
 

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well, the device would basically do what the ECU does on the 88-89 preludes. It would monitor engine speed. Based on engine speed, it would output a variety of signals to some kind of valve control attached to the car's vacuum system. That would allow for a continually variable butterfly setup.

i dunno, though. maybe i'll play around with the idea some more when i get my b20 IM.
 

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yup. you're right. I wasn't thinking. There HAS to be some kind of valve to control the vacuum :p
 
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