Motronic base butterfly position - Alfa Romeo Bulletin Board & Forums

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Old 06-14-2012, 05:06 AM
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Motronic base butterfly position

I was just about to put my plenum back on my TS engine in the GTV tonight, and I thought I would check the TPS function (when I drove the 75 before I wrecked it, it was not idling as it should). As it happens, the TPS was not closing properly.

I adjusted it, but then thought why would it need adjusting? Having a sticky around it looks like someone has adjusted the base setting of the throttle butterfly (opened it up to raise the idle). This may have been to compensate for a stuffed idle control valve... who knows?

Anyhow, as the TPS is pretty hard to get at on a TS, I want to check the base setting on the butterfly and set it right before bolting it all up.

Any ideas how they are set from the factory? Just off fully closed, or should it be done with a feeler gauge?
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Now: 1985 GTV Twin Spark // Past: 8 x 105, 7 x 116, 4 x 900, 4 x 160
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Old 06-14-2012, 06:11 AM
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I'm not sure about the TS specifics, but other systems I've set up need the throttle stop screwed in a bit at least, just like a carb.
The idle air solenoid is so the ECU can adjust the idle speed within a range, but it's not designed to flow all the air at idle.
If it was, there wouldn't be a throttle stop fitted on the butterfly, they'd just be pre-set to close right up.
If when you get it back together you find that the revs hang when you lift off the throttle, that's a likely sign that you need to open the butterfly a bit more.
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Old 06-14-2012, 03:53 PM
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I think I will adjust it so that the stop screw looks like it in the original position (making sure the butterfly is not binding in its bore), and then adjust the TPS.

I would say that the idle air soleniod should be working at the lower end of its range (25% duty cycle) when the engine is idling at fulll temperature (this allows for maximum compensation to lift the idle speed when cold or the air-con is on). When it is all running and at temperature, I would say that I should be able to disconnect the idle solenoid and have a drop from ~850 rpm (I think that is stock), but not fully stall.

Can someone out there with a running stock TS do this experiment for me?
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Now: 1985 GTV Twin Spark // Past: 8 x 105, 7 x 116, 4 x 900, 4 x 160
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Old 06-15-2012, 01:55 AM
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The throttle bodies are adjusted for a certain flow at the factory and secured with a drop of paint. They are a never touch item, following the manual.

To get it right again when the butterfly stop has been disturbed or other cams are fitted(!), there is a procedure that was released as a service fix for other cars with the same injection system and components.
Be sure there are no leaks behind the butterfly. Check all connectors and hoses for cracks and fallen of parts. It is a good idea to renew them as they are very aged now and all have gotten very brittle, sometimes only at one end. Often they only stick to there position, letting false air in.

Basically with the engine at working temperature (cooling fan has started for 2 times) you disable the idle solenoid (or IAC valve =idle air control valve) electric connector and completely turn in the idle adjustment screw. Disconnect the O2 sensor signal cable.
Then you open the throttle stop until the car has a basic, low idle at about 650 rpm, but does not stall. The butterfly must be lifting a tiny in any case, to prevent it from sticking and wearing. If you need not to open it at all, there is a false air problem to fix!
If done, secure the throttle stop with paint.

Then adjust the idle to 750-800 rpm with the idle screw. It should react very spontaneous.
Last, connect the electrical connector to the IAC. The idle should be rising a few rpm (about 50) and be very stable at 850. Reconnect the O2 sensor.
It can be unnecessary to disconnect the O2 sensor for the procedure, if no stable idle can be achieved this way.
A bit of oscillation of idle rpm can not be avoided with most engines, because the O2 sensor makes for a permanent change from rich to lean, which is right if anything is OK.

If there is still no satisfying idle, independent of engine temperature, the CO may need some adjusting too. If you follow the manual, you have to use a CO tester connected in front of the catalytic converter and set it to about 1.0-2.5 % CO without Sensor connected to the ECU. But usually this setting is OK. All together a job for experienced mechanics that have a feeling for engines.

There may be other procedures for this task, but they all have the same aim: Get the adjusting devices, to operate at their best basic setting. Because the O2 sensor and IAC are disconnected, there is no active correction and you are automatically going for the best setting if you follow the instruction. Only if this setting is right, the IAC can perfectly control the idle , because it follows a map and works the better the least correction it has to make to the preset duty cycle. A basic workload has to be seen, that is why the idle set by the idle screw has to be a bit lower than the programed target rpm in the ECU. It can be neccesary to find the IACīs sweet spot with the help of the idle screw. But IAC connected and not connected have to make a difference in idle RPM.
The numbers given may vary a bit, depending on the instrument that measures RPM. If your cars manual shows other values, use them.

All basics like valve lash, cam timing, ignition parts, air filter, compression, etc. have to be in good working order prior to doing this adjustment, please!


With performance cams there may be no idle at all until you adjust the throttle stop, as these can affect the AFM because of strong pulsations!
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Old 06-18-2012, 01:27 AM
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PS the throttle position switch may need adjusting after the procedure just described.
This is not critical, as it should be right when it is made to make contact with the spindle against the throttles opening direction, so there is no slack. Must be done without any force. Then carefully fix the screws while holding it. It has to open simultaneously with the butterfly. The separate micro switch, if there is one, has to make an audible "click" as soon as the throttle starts to open a degree.
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Old 06-18-2012, 04:40 PM
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AflfistaChris: Read my profile!

A simple confirmation that this sounded like a reasonable method to reinstate the base butterly position would suffice with launching into an information overload (with a few inaccuracies thrown in) would suffice.

While your responses are meant in the best intent to educate the great unwashed, they are verbose and generic to the point of being confusing and contradictory.

I mean this in a constructive way. Keep your advice clear and to the point. And write for your audience. Generally people that are reading a thread such as this will have some idea about engine management.

BTW: anyone out there with a healthy 75 TS willing to make the 5 minute experiment for me?

The answer should take the form of "### rpm"
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Old 01-17-2013, 03:47 PM
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The solution!

Just thought I would make and addition/update to this thread I started an eon ago for those that may be interested.

I found the instructions in the 75 TS workshop manual that describes setting the base butterfly position... It went something like: use Solex tool XYZ, adjust air flow through butterfly to X.... In other words, the position is set using a special tool that measures the air flow while the butterfly is not on the engine. This was not going to help me...

First of all, I tried to set the butterfly at a position just cracked open... this did not work! The engine would stall when revved and when allowed to come to idle.

So I sat down and worked out how the system works and reasoned it out:

The ICV should be lifting the idle from a base flow setting of the butterfly as is demanded: Cold engine, airconditioning on, loads place on the engine by power steering and alternator. So in theory, to give the ICV the most capacity to lift engine speed for warm up and other demands, the base butterfly position should be set up so that it is just below the pre-determined idle speed (i.e. that is: when the ICV is closed).

The problem in adjusting this is that it not just a matter of disconnecting the connector off the ICV and adjust the idle speed. When there is no power to the ICV, it is not actually closed: it is open a certain amount as the rotary part of the valve turns back on itself to a position that is slightly open (I think this is a design feature to assist starting, and prevent stalling in the event such as above). So I blocked all flow through the valve and adjusted the idle while the engine was hot to about 800 RPM (then adjusted the TPS position).

Initially this was great.... worked a treat. Then after a few drives while sorting out other stuff, the engine would initially idle at around 1500 rpm, then surge up and down when it got hot. After a few checks and pulling the TPS on and off (horrible to get to!), I found the TPS idle contacts were only working intermitantly. Last night I found the issue: There was a poor solder joint between the idle micro switch and pin inside the TPS. Sorted it out and voila! Obviously, this problem is why someone had messed with the butterfly in the first place (I bought the 75 T-S engine in a repairable write-off).

So the answer was: There is a special tool that was used at the factory, but probably no one else would have. To set a messed with butterfly:

1. Warm engine
2. Block all flow thought ICV
3. Turn off all ancillaries
4. While engine is running, adjust idle stop screw so that the engine idles just below factory setting.
5. Unblock ICV.
6. Set TPS.
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Now: 1985 GTV Twin Spark // Past: 8 x 105, 7 x 116, 4 x 900, 4 x 160
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  #8 (permalink)  
Old 01-17-2013, 04:25 PM
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Quote:
Originally Posted by Clayton105 View Post
When there is no power to the ICV, it is not actually closed: it is open a certain amount as the rotary part of the valve turns back on itself to a position that is slightly open (I think this is a design feature to assist starting, and prevent stalling in the event such as above).
Yep, it's so that an engine with a failed ICV will still run (but idle a little fast) - if it failed in a closed position, you'd risk stalling every time you turned on the air conditioner

And dodgy idle contacts would have made it rather fun to try and set up properly for sure
Did it log any fault codes for the idle switch?
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Old 01-17-2013, 04:44 PM
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Quote:
Did it log any fault codes for the idle switch?
Probably... As I had been mucking around a fair bit, I knew that that would only lead me astray, so I didn't bother looking. I should check and clear them.

I still have not got the car registered. A few things still to do...
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Old 01-17-2013, 05:05 PM
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But if you'd cleared them and the idle contact fault came straight back, it might have actually helped you find the problem

But if it was me, I'd have probably thought "stupid computer doesn't know what it's on about" and hacked the firmware to disable the fault code completely - and then spent ages trying to work out why it wouldn't idle
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