Anyone successfully install an idle air control valve with PMO ITB's?

[Cloggie]

Getting close to assembling the engine, it will be a joint effort between me and a local shop who will oversee my work as this is my first engine build.

Anyway, engine is a 3.4 l with the high compression Mahle P/C's, dual plugged, Rasant system with CoP, Dougherty DC 35 cams, Eisenmann exchangers and CarGraphic exhaust.....and of course PMO ITB'S controlled by a Motec M130.

The tuner tells me that the PMO's are quite good, but they are not the best at idling due to the rapid change in airflow as the throttle plates move off of the rest position...and he asked about an idle air control valve. He said if I want an idle below 1000 rpm and especially with low temperature (like below freezing), the ITBs could not do it...and I don't like high idling for a number of reasons.

I checked out a bunch of threads on this forum and there is no conclusive answer or even a successful install of an IACV for any ITB set up.

My current thought is to use the Haltech IACV tied into the little ports on the PMO's that the MAP will use, but I worry about disturbing the MAP signal, albeit only at idle as the Motec would close the IACV at anything over about 1200 rpm.

So, very curious as to experience by anyone with this. I see the GarageTime guy on YOUTube (great channel) is going to do this but has not yet, so looking for anyone who has done it successfully and is willing to share the parts used and the set up.

Much appreciated and I will post my experience once I get that far....have another work gig coming up, so I may end up being on the road again pretty soon.....

D.

[thetorch]

IACs work great with alpha-n.

With speed density tuning, IAC can create noisy MAP readings at idle, as you point out.

Pretty sure the M130 can do hybrid alpha-n/speed density so you can transition to MAP above idle.

[colingreene]

The motec should have a micro adjust feature for idling on multi throttle plate motors.
just have to find it in the settings. you are running a E throttle correct?
thats what I understand from your post.

[Cloggie]

Originally Posted by thetorch

IACs work great with alpha-n.

With speed density tuning, IAC can create noisy MAP readings at idle, as you point out.

Pretty sure the M130 can do hybrid alpha-n/speed density so you can transition to MAP above idle.

This makes sense to me, especially essentially ignoring the MAP signal until off idle.

Now I just need to find the best IACV to use, the plumbing is straightforward as I have the PMO manifold and it is just passing air which is easily drawn from the air cleaner.

I am digging into the Bosch IACV as we speak...

Thanks for the good thinking....

D.

['78 SC]

Like the OP, I'm in the process of building an EFI engine with ITBs. The manufacturer of my RHD ITBs recommends using an idle air control valve, but with a throttle position sensor and Alpha N tuning rather than MAP and speed-density. The ECU controls the IACV duty cycle and has a table to control fueling based on the IACV duty cycle.

[Cloggie]

Originally Posted by colingreene

The motec should have a micro adjust feature for idling on multi throttle plate motors.
just have to find it in the settings. you are running a E throttle correct?
thats what I understand from your post.

No, just manual linkage, no e-throttle.

I will dig into the Motec for the micro adjust feature you mention. I assume it allows for finer cell sizes at the small throttle opening positions which (if I imagine correctly) would allow micro-tuning as the plate swings off of the idle position into the more wide open position.

Thanks for the heads up....I have not gotten into that level of detail with the tuner...I will chat with him.

D.

[winders]

With drive-by-wire (electronic throttle) and MoTec M1, you would not need or want an IAC setup. Just set the target idle at various head temps as the engine warms up. This is so much better than a manual linkage pedal setup....

I don't get trying to use MAP with ITBs...

[Cloggie]

Originally Posted by winders

With drive-by-wire (electronic throttle) and MoTec M1, you would not need or want an IAC setup. Just set the target idle at various head temps as the engine warms up. This is so much better than a manual linkage pedal setup....

I don't get trying to use MAP with ITBs...

That is an interesting point and it is not too late for me to make the change.....I definitely do not have anywhere near your level of experience so curious why you think that the MAP/ITB combo is a poor choice.

Of course it begs the question as to what is a good e-throttle for a G series (1989) 911 in terms of fitting in that rather crowded footwell and which is a good match for the Motec. I have zero problem with fabricating the mount in the engine compartment and the wiring is not a worry...just one more cable to thread through...

The idea has some charm for sure....

D.

[Showdown]

It sounds like this may be a particular quirk of your engine build. With RHD ITBs and using MAP, I was able to get a solid 900 rpm idle without much trouble. I have a hand throttle for start up and extra cold weather, but that’s only needed for the first five minutes or so.

It might be worth rigging up some simple plumbing to test this idea before purchasing the IACV and running all the wiring. Some simple plumbing fixtures and valves would likely suffice as a proof of concept.

[Cloggie]

Originally Posted by Showdown

It sounds like this may be a particular quirk of your engine build. With RHD ITBs and using MAP, I was able to get a solid 900 rpm idle without much trouble. I have a hand throttle for start up and extra cold weather, but that’s only needed for the first five minutes or so.

It might be worth rigging up some simple plumbing to test this idea before purchasing the IACV and running all the wiring. Some simple plumbing fixtures and valves would likely suffice as a proof of concept.

Yes, also a great data point and a good approach.

I have a bit of a bias to just install the system as Rasant designed it and see what happens. I fully expect the motor to be in and out a few times over the coming year and as you rightly point out, the IACV or e-throttles are additive components and are quite easily fabricated in terms of mounting and wiring, only material change required is Motec configuration.

I am also wondering about the DC35's - John Doherty was quick to recommend those when I gave him my targets for the engine build which are (in order) reliability, durability, drivability, fuel economy, compatibility with Cats...max power is not really a concern for me at all.

His view was these (on a 3.4) will be nice, crisp and not especially lumpy at idle...which ought to be a good predictor of idle stability.

But many thanks to the thoughts from all on this thread, your collective input is most definitely helping to shape my thinking.

D.

[rwest]

If you are using the PMO ports to get a MAP reading for your fueling and then try and add idle air to the same ports, it is like a huge vacuum leak and you won’t be able to tune for cold and hot idle.

I’m currently in the same situation and my next step is going to be to see what happens if I add idle air to the brake booster port (just as a proof of concept test) and what happens to my MAP readings when air is added to the opposite side of the ITBs and if it changes readings.

I am also thinking of just trying to tune using the throttle position sensor, which would then let me use the existing ports to add idle air.

I’m using the IAC from a Jeep if that helps.

[Showdown]

FWIW, and no I don’t run an IACV so take it with a grain of salt, but clustering my throttle body vacuum ports together in two banks (123, 456) and then clustering those into a manifold helped stabilize the MAP reading a lot. I’d recommend 1.) making the port hoses as small as possible, like 1/16” or 1/8” down from the 1/4” that they probably are now, and using a foam filled manifold (if you can) as it all helps limit the air leak to only what’s necessary and limits the pulsing that can sometimes wreak havoc on MAP signals… my guess is that might also mess us the IACV…

[jj911c2]

I have a PMO/Infinity ECU/MAP block setup on a 3.8. I can idle fine at about 850 RPM without an IAC. Where I have trouble is the first few minutes after starting it will struggle to idle in the cold. I have considered adding an IACV, so watching this thread with interest.

[thetorch]

Originally Posted by winders

With drive-by-wire (electronic throttle) and MoTec M1, you would not need or want an IAC setup. Just set the target idle at various head temps as the engine warms up. This is so much better than a manual linkage pedal setup....

I don't get trying to use MAP with ITBs...

Edit: upon reflection, I get it. You are saying DBW operates the throttle bodies, so air and fuel together can manage the idle. That makes sense. If you don't go DBW, IAC is really nice to have IMO.

(earlier version of post below ...)

Scott,
I am confused why DBW solves this when you can inject fuel amounts for various CHTs regardless of manual linkage position?

The IAC solves the issue of having nearly closed throttle plates for happy warm idle, which doesn't work well for cold start and warmup or unusual situations.

Just setting target idle using fueling is not easy in my experience with ITBs, unless you enjoy running high idle or using a hand throttle for cold start and warmup, which works well of course.

I run alpha-N with an IAC and it's fantastic cold hot or anywhere in between. Why would a DBW make it better?

Though maybe I am missing something.

[Chris78]

I have 2.2 with MS2 and PMO throttles.

First 5 minutes I modulate with go pedal to keep rpms up a little then idles fine. Same in cold weather just takes a bit longer.

I've also read alot of people use the hand throttle and that works perfect for cold start idle.

[winders]

Originally Posted by Cloggie

That is an interesting point and it is not too late for me to make the change.....I definitely do not have anywhere near your level of experience so curious why you think that the MAP/ITB combo is a poor choice.

Of course it begs the question as to what is a good e-throttle for a G series (1989) 911 in terms of fitting in that rather crowded footwell and which is a good match for the Motec. I have zero problem with fabricating the mount in the engine compartment and the wiring is not a worry...just one more cable to thread through...

The idea has some charm for sure....

D.

The problem with MAP and ITBs is getting a reliable and meaningful MAP value. You can use a blended method of using MAP at lower RPMs and relatively closed butterflies. But, as soon as you start flowing a lot of air, the vacuum goes away so you need to use Alpha-N when the RPMs go up and the ITBs are open more. I wonder why one would bother with the vacuum lines and vacuum reservoir required to get a stable vacuum to measure. Alph-N works great all on its own with ITBs.

I am sure that there are a variety of pedals you could use. I think that a lot of people use BMW street car DBW pedals for this.

Here is what I did:

https://forums.pelicanparts.com/porsche-911-technical-forum/1143466-drive-wire-solutions.html

[rwest]

Originally Posted by winders

The problem with MAP and ITBs is getting a reliable and meaningful MAP value. You can use a blended method of using MAP at lower RPMs and relatively closed butterflies. But, as soon as you start flowing a lot of air, the vacuum goes away so you need to use Alpha-N when the RPMs go up and the ITBs are open more. I wonder why one would bother with the vacuum lines and vacuum reservoir required to get a stable vacuum to measure. Alph-N works great all on its own with ITBs.

I am sure that there are a variety of pedals you could use. I think that a lot of people use BMW street car DBW pedals for this.

Here is what I did:

https://forums.pelicanparts.com/porsche-911-technical-forum/1143466-drive-wire-solutions.html

Scott,

Are you also using the TPS to control ignition advance and if not, how are you controlling it?

Thanks,
Rutager

[Cloggie]

OK guys thanks for all the input.

I educated myself yesterday via some reading, some YouTube and am a little smarter than I was.

Alpha-N is a bit of a misnomer, all it means is that throttle position is the key determinant for the proxy for engine load, versus MAP as we have been discussing.
Also, if I believe High Performance Academy, ITB's literally flow close to atmospheric at anything past 30% open and from that point forward, the MAP signal is more or less irrelevant as a proxy for engine load.
Everything I used to educate me suggested Alpha-N - in most cases only Alta-N for ITB's, but in some using MAP at small throttle openings blending into Alpha - N.

Recommendation seems to be to have very small increments on the load (throttle position) axis, with perhaps 6-8 rows covering from 0 to 20% and then another 6-8 rows covering 20% to WOT. with MAP being optional.

So, considering first of all that I have all the equipment to to MAP or Alpha-N and have already set up manual throttle linkage, my first step is to make use, as was suggested, to use MAP at very small throttle openings blending into Alpha-N higher up and see how that works. It certainly ought to be good enough to get me through the break in period and get some miles on the engine to see how it behaves and idles.
I was planning on using small hoses - equal length - from the ITB ports to the manifold - I think mine are 2.5 mm and have some open cell air filter foam lying around that I could use to help act as a damper in the manifold. Good idea Showdown!

If it idles acceptably - and yes we will use ignition timing to help the idle and with the AC - then all is well.

If I am not happy, next step is to do the e-throttles. Yes, it'd be a little bit of a project, but like I said, the engine will likely have to come out at least once and I do all my own fab work, so worst case I just remake some stuff or 3D print it up and there we go. I am retired after all.

I am digging into Motec software this weekend and ought to be a little smarter on that, if nothing else to make sure I can make informed decisions on what my tuner is recommending.

This thread and the contributions from you lot have been immensely helpful and informative - thank you all.

D.

[winders]

Originally Posted by rwest

Scott,

Are you also using the TPS to control ignition advance and if not, how are you controlling it?

Rutager,

I am not the one doing the actual MoTec M150 (MoTec USA Sportscar package) tuning. I have a professional tuner doing that. I know that timing is changed based on RPM and I would assume there is some amount of timing change based on throttle position as well but I don't know for sure.

[Showdown]

One thing that is critical to using MAP is scaling your fueling table appropriately which was touched upon here briefly

My VE table has the first 6 rows go from 35 to 80 and the next 6 from 80 to 100…. This allows for using MAP more effectively than with linear scaling and creating a table that is very usable.

Don’t give up on MAP- yes it’s slightly more work to get it just right but it’s a fun process and you learn a ton about the car.

In addition you have to decide on closed or open loop tuning- but that’s a whole other conversation.

It’s also worth keeping in mind where you plan to spend most of your driving time and allowing for more cells in your table in these areas; ie: I’m hardly ever at WOT and 7000 rpm’s so if that part of the table falls off the map (or below 35kpa let’s say) the computer will just give a linear interpolation and while that may not be perfect, it can allow for perfection where I spend 90% of my driving time such as 3000-5000rpm and 50-90kpa, etc…

This may be different if you’re racing but for most of us who aren’t it’s a completely logical approach; tune the car you drive for how you drive.