IAC with ITB will cause problems ?

Patriq Backlund · Post by **Patriq Backlund** » Tue Jan 31, 2006 6:57 am

I'm about to install MS in a car that has ITB originally. Each TB has a small port where a hose from the IAC comes in. These ports enters under the flapper in the TB.

I've concluded that I won't be using these ports for MAP. Experiences from other with the same engine and MS says the vaccum signal won't be stable enough. There for I will be running alpha-N

I've scoped this entire forum, FAQ, and other articles for help - but has not found any solution so far.

My question is:

If I continue to use these small ports for IAC with MSII, won't that mess up calculations for MS/MSII ?

I'm thinking - the original set up has intake manifold mounted on top of these 4 ITB feeding them with air from the airfilter box. Directly after the airfilter box and before the manifold is the AFM. The IAC takes it's air from the manifold. This means that any extra air going to the engine via the IAC is measured and calculated for by the ECU (with data from the AFM).
If I now feed extra air via the IAC - the MS/MSII won't have a clue that this extra air enters the engine - and hence won't calculate correctly.

I'm a right or wrong here ?

(and also if anyone has hints of where to find info on how to tune with alpha-N, I'd be very grateful. I'd scanned the Tuning-forum too. And I can't find any info on the differences on how to use the tuning software with alpha-N instead of with MAP. All that it says under info on Tuning is that the procedure described only applies for using with MAP and not alpha-N)

Kind regards,

milesinfront · Post by **milesinfront** » Tue Jan 31, 2006 4:25 pm

I'd stick with map... Look at adding some dampening to the pulse, like restrictors and/or buffering tanks. When the itb's cause complete loss of vacuum at small throttle openings/low revs is the map sensor lying to MS??? No it's not, the engine is really at full load!!!

But even so, I think with Alpha-N you will still be okay with the idle control. Your idle mixtures will be dependant on rpms, so you may just need some extra rpm boxes down low. e.g. 500, 600 & 800 depending on your desired idle range...

Patriq Backlund · Post by **Patriq Backlund** » Wed Feb 01, 2006 1:31 am

Hi !

Thanks for the answer. I've been thinking the same way as you - with dampers. But using these small ports will outrule using IAC - since I'm using the only ports available for IAC. Meaning I can't control warm up idle.

and....

I'm still wondering about how the extra air that comes into the engine will effect how it is running. Especially at idle. Since the air that comes into the engine does so without MS knowing of it - wont the stochiometry be wrong?
Since MS assumes the air/fuel ratio is something else (since it has calculated that with closed throttle and 'n' rpm the mixture is 'x'. But it isn't, since air "leaks" in via these small ports - held open by the IAC.)

milesinfront · Post by **milesinfront** » Wed Feb 01, 2006 1:58 am

You are correct, MS will not know of the change in air, but i'd be kind of optimistic as to how that will really affect things in actual operation...

If you go for a fast idle at warmup, then the rpms will be higer, so you'll be able to tune that box. Then your normal temp idle speed will have it's own box. As far as closed loop idle speed goes, I THINK the amount of change in air will not be big enough to really hurt things...

My race car has a really stable idle just by making a dip in the timing curve. 500rpm is 12BTDC, 800 is 10BTDC and then 1500 is 12 again. The engine seems to find a spot (800-900rpm) and sit there happily. I don't have a cold start valve, so the engine idles 100-200 rpms slower when cold, but it never even looks like stalling. You never know, I may be blest, but it works for me. I can remember some talk about using timing to actively control idle speed, so it really is a useful tool...

You also do a similiar dip with fuel. It just means that when the engine slows a little, then the timing advances a little, which in-turn pursuades the idle to lift. If you get the balance right, then you will have a steady idle with no hunting...

Patriq Backlund · Post by **Patriq Backlund** » Wed Feb 01, 2006 2:27 am

Hi !

Thanks - that was helpful !

I think I'll try without IAC then. And go for MAP after all.
(I've only soldered the board so far - and am setting up all sensors etc. within a week or two.)

Regards,
/Patriq

milesinfront · Post by **milesinfront** » Wed Feb 01, 2006 3:03 am

what is that car anyway???

Patriq Backlund · Post by **Patriq Backlund** » Wed Feb 01, 2006 3:17 am

The one in the avatar, or the one I'm squirting ?

The avatar is my Alfa Romeo Junior Zagato. I think they built 450 of them. Mine is a 1970.
The one I'm squirting is a Alfa Romeo 33 Q4 Sportswagon - 1993. It's got a 1.7 16V boxer engine. Same engine as in the Formula Boxer series.
I also have a 1984 GTV6 with a 3.0 V6 in it. I have a Link-system for fuel and spark for it. Haven't installed yet though.

By the way - are you staying up late ? Australia !

Regards,
/Patriq

milesinfront · Post by **milesinfront** » Wed Feb 01, 2006 3:21 am

Nice looking car... (Avatar)

It's only 8.21pm here, and mom said I can stay up a little later!

Patriq Backlund · Post by **Patriq Backlund** » Wed Feb 01, 2006 5:53 am

Thanks !

You can read more on them at www.zagato-cars.com
They are extremely nice. Aluminium chassie, discbrakes all over, low wheight. Resonably stiff and low drag.

Oh.. I thought it was later "down there" ?

Regards,