Magnum Powers 85mm Throttle Body Question

Super XR7

Registered User
On the Magnum Powers 85mm throttle body, what is the function of the set screw that is near the idle air control circuit?

Mike
 
Looks like a air bleed screw to control air between the top and bottom
portion of the air-by-pass chamber.

I have a question. On the set screw that adjust the throttle body
lever for the butterfly inside the throttlebody. mine was ground off
so no adjustment can be done for setting idel on my car.

Randy
 
Randy N Connie said:
Looks like a air bleed screw to control air between the top and bottom
portion of the air-by-pass chamber.

I have a question. On the set screw that adjust the throttle body
lever for the butterfly inside the throttlebody. mine was ground off
so no adjustment can be done for setting idel on my car.

Randy

Randy, my throttle body does have a screw to adjust the butterflly and I bought it back in mid 94. On the set screw when would one need to adjust it, and what exactly does it do??

Mike
 
The set screw that adjust the butterfly plate.And how I have used it.

I adjust screw out, until butterfly plate in throttle body is completey closed.

Then I loosen the screws on my TPS throttle position senor.Turn the TPS
until it reaches .95 on volt meter.measureing volts from the middle wire
on the TPS wire plug in. After reaching .95 volts Then tighten the TPS screws.

Then I start my car let it warm up.And then use the adjusting screw
that adjust the butterfly plate in the throttle body.I make 1 1/2 to
up to 3 turns or more to get the car to idle at around 850 rpms.

This is how I set my TPS voltage and set the idle that I need.

I have not installed my 85 mm MP throttle body because I see no
way to adjust it for me to be able to get it to ever idle right.

Randy
 
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Shouldn't you un-plug the IAC before you set idle (so that it can't work against you)? I did mine by unplugging the IAC, then setting idle to about 600 (just until it's smooth, but a little lower than normal). Then plugged the IAC back in and, good to go.
 
Guys, thanks for the help. I am going to work on getting my car to idle at the correct rpm and yes I would first disconnect and block off the idle air circuit to get a base idle, from there work on the idle air control circuit parameters. I really am not sure what this set screw does.

Mike
 
That screw is an additional air bypass. The throttle blade is not supposed to be adjusted to acheive base idle. The throttle blade is supposed to be adjusted only to the preset amount. If that is not enough to achieve a base idle then the bypass screw is to be opened enough to achieve base idle and then the IAC will control the remaining amount. If an IAC valve is being asked to control too much of the total amount of air required for idle then idle stability issues will result.

That is of course if you are talking about the rather large set screw that faces the sky on the inboard side of the TB next to the IAC.

And no, I'm not sure why you can't just use the throttle stop to set base idle speed other than the fact that doing so will make the EEC think that you are opening the throttle. I've done it both ways before and it seems to work.
 
XR7 Dave said:
And no, I'm not sure why you can't just use the throttle stop to set base idle speed other than the fact that doing so will make the EEC think that you are opening the throttle. I've done it both ways before and it seems to work.

If you use the set screw connected to the butterfly to adjust idle.
you will no longer have a voltage set of .95.. If you use this screw
to raise idle,you will also be raising the votage of the TPS.

The reason why I used the butterfly screw for adjustment of the idle.
Was because I could not break loose the air-bleed set screw located
above the IAC.To get it to be adjustable.

David D. is right, using the butterfly set screw will work,but it
raises the TPS voltage.This will make the EEC think the throttle
is slightly open.

This is how I have adjusted the set screw to make sure the butterfly
plate is closed.You do this before setting the TPS voltage.

1.Turn screw until it no longer is touching the stop on the throttle
cable arm that connected to the butterfly plate.

2.Place a peice of notebook paper between the screw & throttle
cable arm stop.

3.Turn screw until you have drag on the peice of paper while tring
to pull the peice of paper out from between the stop and screw.
If the paper pulls out with slight drag.You have the throttle butterfly
plate properly adjusted.

4.Then you can start the adjustment of the TPS voltage to .95..

5.Then you use the IAC air bleed screw that you ask about in your
first post. To adjust THE IDLE on your motor.

I was never able to follow DR. Freds instruction and get my car to idle
right.

Randy
 
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There is a command in the EEC that tells it when the throttle is open beyond idle. It is a change of about .1-.2v over base setting. The EEC reads base setting every time the key is turned on so it should learn just about any value up to a point (in OE fashion the EEC has redundancy built in on just about every circuit and we only have access to some of them). However, there is no way for the EEC to understand what you are doing with the throttle blade while it is running so adjusting the throttle blade while running can cause goofy things to happen.

Regarding actual setting of the blade, the proceedure says to back the screw off .010" and then turn it down 1 full turn (going off memory here since I rarely do it that way). Essentially the universal rule for setting any throttle blade is that you never want it totally closed. You always want at least some air moving past the blade. Exactly how much I can't say and it may not even be that critical. I do know that there is a value in the EEC that specifies the amount of air that is bypassing the throttle blade. If you alter this then values don't match and well, you can see where that is heading.

Unfortunately we do not have access to all the parameters that the EEC uses so even if you want to you can't set everything exactly "by the book" and so a little bit of "jury rigging" has to be done even in the best of circumstances.
 
This is getting a little bit amusing, because there is no way something this simple should be this complicated. LOL

Just for what it's worth, note that some Fords actually have holes drilled in the throttle blade to ensure some air bypasses the throttle blade. My mom's 1996 Windstar 3.8 splitport had this.
 
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