Adding IAC to a downdraft setup

[mwarchut]

I have an 8 stack downdraft intake. I've got the car running pretty well except for one issue. If I have the throttle plates closed all the way and the TPS calibrated to 0 from dead cold the car will not start unless I open the throttle a bit. Once its warmed up it will stay running with the throttle plates in this closed position at around 900 RPM. If I crank the plates open a little with the stop screw, about 4% or so, the car will start cold but the idle even warmed up never goes below 1300 rpm, until I close the plates a little at the stop screw.

Someone suggested that I may be at the end of the mechanical limits of the throttle body and need to add an IAC to get extra air into the system while it is cold. Is there a way to do this on a downdraft intake? It does have a vacuum plenum that leads to each TB. Could I just plumb in an IAC to some sort of distribution block and then put that in line with a vacuum line? Or is there a mechanical way to do this from the throttle links? or? Thanks all... this has been quite a fun and educational experience.


Michael

[billr]

A simple solenoid to provide a secondary stop for the throttle shaft should do the trick, they were common back in the carb days to kick up the idle when A/C was on. You would use the standard MS PWM "fidle" feature, but program it for just on/off operation. Note that I am talking about a solenoid actuator, not a solenoid-operated valve.

[nathaninwa]

I've used those solenoid actuators before to raise the idle while winching in my wheeler

[mwarchut]

Thanks for idea billr! I like that one a lot more. I wonder if Morgan's in WC can hook me up with something. I just noticed you are like 15 minutes away from so I had to throw that in..

[billr]

Sure, Morgan's may have them, but most other parts stores will also. It looks like they are commonly called "Idle Stop Solenoid" (go figure!). NAPA shows quite a few, ranging from $23 to nearly $200, so you want to be selective in what you design around. The old Chevy one I have lying around is P/N DR1114418. Search for that number and you will get a lot of hits, so that gives some place to start from.

[mwarchut]

The most insteresting part is going to be to figure out how the sanest place to put it. The throttle linkages have two stops on them now. One onf the left 4 ITB's and one on the right 4 ITBs. Currently only the one on the left is actually being used. I could put the solenoid on the right side near the lever where the stop is. Ill have to track one down with a bracket of some sort that I can modify to bolt to the existing holes. Or make another bracket like I did for the Lokar throttle cable. It's always something... LOL

thanks again

[billr]

One more note, those solenoids may not have enough pull at the beginning (de-energized) end of the stroke to pull the throttles open. You may have to open the throttle slightly before cranking, to let the solenoid extend freely and get set in place, then you can release the throttle and let it come back to the solenoid stop and start cranking. Once the solenoid is extended it will have plenty of pull to keep in place. I'm probably making it sound more complicated than it is, just a quick blip of the throttle right after key-on and just before cranking will do it.

Oh, yeah, since this is just to open the throttle while starting, I think putting that solenoid stop on just one throttle shaft will work fine; no need to worry about any slop in the linkage holding the shafts in slightly different positions. I expect, though, that you have little slop anyway, so that the throttles are synced in normal running!

[mwarchut]

Thank you for sharing your experience. It is greatly appreciated. I started this project last fall and then had to put it on hold because of surgery and then other priorities. I want to get my cobra out and drive it around before summer is over. After this week all of my other priorities will be met and this will move to the top.

[pkm123]

I have a 8 stack setup that is similar. A picture of your setup would help. My intake has a common plenum where I measure MAP and use the vacuum for the brakes. I added a Ford Idle air valve that is plumbed to the plenum. This adds air when the engine is cold and also runs closed loop idle control. Ford also used a on/off valve in early mustangs that could work. Are you running Alpha-N or SD?

[mwarchut]

The intake does have a vacuum setup. All 8 runners have a tap hole that leads into the center of the manifold. They sealed off the center of the manifold with an aluminum plate and a gasket. On the top they have two threaded holes that accept a small NPT style fitting. Right now one is plugged and the other has a fitting that I have connected the MAP and fuel regulator to. The other I was going to connect the brake booster to. How large of a fitting would be needed to flow enough air this way? I do see a way that I could drll and thread a larger one on the back of the manifold if need be.

Oh and I have it set to ITB in the MSII. So it uses a variation of Alpha and SD.

[pkm123]

The fitting needs to be about 1/2 inch in diameter. I used a -8 AN pipe thread fitting. A picture of my setup is in Success stories under "452 cu. in. FE". My manifold had a pipe plug at the front of the manifold. I put the fitting in the plug hole and attached a aluminum block to the other end. I then mated a Ford Idle air control (solenoid) from a late model engine to the block. Then I reduced the butterflies to almost closed and let the idle air flow through the plenum. The engine will idle down to 600 rpm, but I use closed loop idle to maintain it about 800 when hot. Do you have a ITB flow sync guage? On mine the Throttle bodies flow about 6 without the Idle air control and 4 1/2 with the control. This setup also allows me to idle at 1000 when cold and decreases as the engine warms. You can drill and tap the manifold anywhere it is convenient and doesn't interfere with the throttle linkage.

In ITB mode the MSII will automatically correct the AFR as the idle air control changes.

[mwarchut]

I do have a flow gauge. I used to have Webers on the car. If I get an IAC that is PWM I will have to modify the MSII to a TIP120 mod right? Or will the basic circuit handle it?

Thanks for the all of the information.

[pkm123]

I'm not sure which version MSII you have. The PWM idle circuit is usually enabled through the FIDLE port which has a power transistor to handle the current load.

[mwarchut]

It is an ms2 3.0 kit I got from diyautotune. It seems that I need to hook the valve up to keyed 12V and the ground side to the relay board. But unclear whether I need to do that upgrade. I can ask them at diy.

[mwarchut]

So a friend of mine had an extra IAC valve kicking around. It is a 2 wire unit. He said it was in a Mercedes. It is a Bosch 0 280 140 510. It looks like brand new. Is that a PWM valve? I have my board setup with a TIP120 mod kit for PWM. When I connect the valve to the MS2 the ECU resets itself. Am I missing something? I put the flyback diode into place. I connected one side of the valve to 12+ and other side to the fidl terminal on my stimulator board. Any thoughts are welcome.

[pkm123]

Sound like you did everything correct. You need to know if the valve in normally open or normally closed. I don't know why the megasquirt would reset

[mwarchut]

Actually I figured out the reset issue. My testing power supply wasn't large enough to handle everything. I switched to 1000W bench supply and connected the 12+ to supply, along with the jimstim. THe negative of the IAC to the FIDLE port on the jimstim. Now the resets have ceased because of the larger PSU. The valve appears to normally closed and when power is applied it opens. When I start the PSU it opens immediately, before I even power the jimstim/MS2. Then when I power he stim I can see in tunerstudio the PWM % is at like 60% with a low idle of around 1000 and temp still cold. As I raise the temp as expected the PWM % goes down however the valve doesn't seem to move at all. It just stays wide open. Shouldn't I see it start to close? Is there an easy way to test that the FIDLE circuit I put in is working? I have a scope and meters if there is a way. I'm branching into unexplored territory here for myself. But its always good to learn. ANd if this doesn't work out I expect my parts for my secondary throttle stop to be here today.. LOL

[pkm123]

usually the Idle air valve is normally open (when powered up), but is closed by engine vacuum. Then the MS2 opens with the PWM as programed.

[mwarchut]

So what you are saying is there is no easy way to bench test this and just putting it into the car is really the only way. Ok. I'm game.

[pkm123]

take a look at this thread. http://www.msextra.com/forums/viewtopic ... 71&t=48680