IAC Valve to Elevate RPM When A/C On

[Uwon]

I’m looking for a substitute/non Porsche replacement to the Pierburg air valve (NLA) used on the pre-Motronic fuel injected motors to increase the idle rpm when the A/C compressor is on. It’s a simplet 12v on/off valve. Anybody aware of a suitable substitute that is reasonably priced?
Thanks in advance.
Cheers,
Johan

[Uwon]

Anyone?

[dap930]

Post up a picture or the P/N of the part you are trying to replace, that may help.

[Jonny H]

You might be able to use one of our CDI+ boxes to do that. Essentially use the box input to advance the ignition timing which would raise the RPM.

We’d have to write some code to do that but if it benefits the community then it will get rolled out for everybody.

Let me know if this is of interest.

[Uwon]

Originally Posted by dap930

Post up a picture or the P/N of the part you are trying to replace, that may help.

Part #36, 911 606 102 01, AX, 04, or CX



Thanks.
Johan

[dap930]

Is that not the AAR valve that adds additional air when the engine is cold and gradually reduces air as the heating element warms the bimetallic lever to close the opening?

[Uwon]

Originally Posted by Jonny H

You might be able to use one of our CDI+ boxes to do that. Essentially use the box input to advance the ignition timing which would raise the RPM.

We’d have to write some code to do that but if it benefits the community then it will get rolled out for everybody.

Let me know if this is of interest.

Jonny, many thanks for your offer but I’m running an Electromotive tec3r engine management system on a 3.2 converted to a 3.4 turbo with low compression ruf pistons and cylinders. The software allows me various adjustments to the Bosch 2-wire IAC including the rpm increase with A/C on, but it is not quite enough to raise the rpm quickly to where I want it to be. Believe me, I have spent countless hours on this. So, this is why I’m looking to add the Pierburg IAC plumbed to my unused 8mm nipple on the throttle body to raise the idle by 200 rpm when the A/C is on. I have already successfully tested that opening the nipple to atmospheric air will have the desired effect.
Johan

[Uwon]

Originally Posted by dap930

Is that not the AAR valve that adds additional air when the engine is cold and gradually reduces air as the heating element warms the bimetallic lever to close the opening?

My understanding from a Porsche mechanic is that this valve, when given 12v power, will open over about 20 seconds and will shut off completely with power off. Makes sense to avoid sudden acceleration jerking.
Johan

[Uwon]

A Porsche mechanic that I know who runs a race car support team has enlightened me on a couple of air valves in the K and J Jetronic motors. So here we go....

Refer to the PET pic below and not the one I originally posted on December 9.

Air control Valve #36 is a Bosch Air valve - about 20-60 seconds to change state - air opening is 18-22mm

The Pierburg valve that I have been looking for is actually 17A in the same diagram. 5-20 seconds to open with 2 8mm nipples. They are similar in performance however #17A is smaller and use a vacuum line that is smaller. (8-9 mm vs 18-20 mm on #36). Both valves are actuated with 12v.

Also fortunately for me, I was also able to procure the Pierburg valve from him.




This is Valve #17A. Note electrical plug on back side.



Hope that I have clarified matters and avoided additional confusion.

Now, I will be using the Pierburg valve with the 8mm nipple which I will connect to an unused 8mm nipple on my throttle body. I have already determined that the throttle body nipple provides enough air to raise the idle about 200 rpm and will provide improved A/C results at idle. Valve will be triggered by the A/C compressor 12v "on" via a relay. I want the valve to open up reasonably slowly to avoid jerkiness when motor is running above idle.

Cheers,
Johan

[Dr J]

Hello Johan

Neither part 36 nor 17a will help you in your quest. Part 36 increases your idle for a few minutes on cold start (duration depends on outside air temperature). After that, it is closed and does nothing else for your idle. Part 17a is designed to keep the control pressure regulator (aka warm-up regulator- part 54) at a lower control pressure to richen the fuel mixture, again during cold start. It operates for about 30 seconds.

What you need is a real idle air control valve. There are 2 and 3 wire valves. When I went EFI, I put a wtb ad on pelican and got a used 3.2 iac that is controlled by the EFI. The iac can replace part 36 and be adjusted to increase idle upon engagement of the ac. Since you have the tec3, I would call Clewitt Engineering and talk to them. Here is one of their universal iac valves:

Universal IAC - Straight [1001-76] - $249.00 : Clewett Engineering, The complete solution for ignition & fuel injection

[Uwon]

Originally Posted by Dr J

Hello Johan

Neither part 36 nor 17a will help you in your quest. Part 36 increases your idle for a few minutes on cold start (duration depends on outside air temperature). After that, it is closed and does nothing else for your idle. Part 17a is designed to keep the control pressure regulator (aka warm-up regulator- part 54) at a lower control pressure to richen the fuel mixture, again during cold start. It operates for about 30 seconds.

What you need is a real idle air control valve. There are 2 and 3 wire valves. When I went EFI, I put a wtb ad on pelican and got a used 3.2 iac that is controlled by the EFI. The iac can replace part 36 and be adjusted to increase idle upon engagement of the ac. Since you have the tec3, I would call Clewitt Engineering and talk to them. Here is one of their universal iac valves:

Universal IAC - Straight [1001-76] - $249.00 : Clewett Engineering, The complete solution for ignition & fuel injection

Thanks Dr 3. I will check the operation of valve 17A when I get it this week and report back.
I already have a Bosch 2-wire IAC (from Richard) installed which operates better than my previous smaller 4-wire unit. It handles the idle well save that the idle up feature on the tec3 when the A/C is on does not do anything (been checked out by Electromotive twice already). Unplugging the unused 8mm nipple on the throttle body provides me with the desired rpm increase.
Cheers,
Johan

[Jonny042]

I think any 12V on/off (normally closed) solenoid will work fine although having one that will open/close slowly is going to be tougher to find.

Since you already have an IAC that's working correctly, have you tried simply opening the air bypass slightly (analogous to setting the base idle) so that the IAC is less open during normal idle (AC off) and then has more room to open when the AC kicks in?. Most modern (well, modern enough to have full EFI control but not so modern that they are drive by wire) control the idle speed 100% with the IAC. If you have enough IAC capacity for fast idle at warmup you should be able to use it to control during AC load as well.

[Jonny042]

Originally Posted by Jonny H

You might be able to use one of our CDI+ boxes to do that. Essentially use the box input to advance the ignition timing which would raise the RPM.

We’d have to write some code to do that but if it benefits the community then it will get rolled out for everybody.

Let me know if this is of interest.

I'll be honest I haven't even looked at the software (yet!!) but since you have the ability to control the timing curve now. As long as you can bump the timing up a few degrees if the idle speed drops below normal idle RPM, you can likely program the CDI+ to do this now?

So for instance if your car normally idles at 900rpm, you could map it to get a few degrees extra advance at 850?

Would be another benefit to the CDI+ that has yet to be explored but since Johan has the tec3 he could do the same if he hasn't already, it might be enough to help his idle issues.

[flightlead404]

I think you are over thinking this. Any old 12v operating pierburg switch will work if you have verified that the port on you TB does what you want open/closed. What you show as 17a I think is a pierburg switch, on the turbo that's used for part of the emissions. There are some square ones called various names like "change over valve", but a google for pierburg switch will find what you want. Gradual change of 200 rpm is not needed. It wants to change immediately when the A/C compressor kicks on/off. Personally I think you should set it up so it only works at idle. There may be a ported connection on your TB that has no effect above idle, or you may be able to tell your software to not open the valve when above 1,500rpm or something.

[Uwon]

Originally Posted by flightlead404

I think you are over thinking this. Any old 12v operating pierburg switch will work if you have verified that the port on you TB does what you want open/closed. What you show as 17a I think is a pierburg switch, on the turbo that's used for part of the emissions. There are some square ones called various names like "change over valve", but a google for pierburg switch will find what you want. Gradual change of 200 rpm is not needed. It wants to change immediately when the A/C compressor kicks on/off. Personally I think you should set it up so it only works at idle. There may be a ported connection on your TB that has no effect above idle, or you may be able to tell your software to not open the valve when above 1,500rpm or something.

Just waiting for the Pierburg valve to arrive so I can test. Also, Jonny042 has already emailed me some non-Porsche inexpensive alternatives that will work.
As you have suggested, the tc3r with the latest Wintec4 firmware does have a number of general purpose output wires that theoretically can control switches/relays under various situations. I already have a relay set up that will cut out the A/C above a certain rpm and below a certain manifold air pressure reading so there are a number of possibilities.
I’ll post my findings in due course.
Happy Holidays
Johan

['76 911S 3.0]

Originally Posted by Uwon

Jonny, many thanks for your offer but I’m running an Electromotive tec3r engine management system on a 3.2 converted to a 3.4 turbo with low compression ruf pistons and cylinders. The software allows me various adjustments to the Bosch 2-wire IAC including the rpm increase with A/C on, but it is not quite enough to raise the rpm quickly to where I want it to be. Believe me, I have spent countless hours on this. So, this is why I’m looking to add the Pierburg IAC plumbed to my unused 8mm nipple on the throttle body to raise the idle by 200 rpm when the A/C is on. I have already successfully tested that opening the nipple to atmospheric air will have the desired effect.
Johan

Why not wire in a vacuum solenoid like a purge solenoid from an EVAP system? Just hook one side to the vacuum source, the other open to atmosphere. You can use a Lowside on the ECU to command this open when A/C on and Engine Speed < 1200 rpm or something along those lines.

[Jonny H]

Originally Posted by Jonny042

I'll be honest I haven't even looked at the software (yet!!) but since you have the ability to control the timing curve now. As long as you can bump the timing up a few degrees if the idle speed drops below normal idle RPM, you can likely program the CDI+ to do this now?

So for instance if your car normally idles at 900rpm, you could map it to get a few degrees extra advance at 850?

Would be another benefit to the CDI+ that has yet to be explored but since Johan has the tec3 he could do the same if he hasn't already, it might be enough to help his idle issues.

Yes, correct. You make a ramp before the idle speed in the timing curve so the ignition will advance when the idle drops.

You don’t get much of an idle drop with the electric AC so I haven’t had to bother with anything like this.

[Uwon]

Originally Posted by Jonny H

Yes, correct. You make a ramp before the idle speed in the timing curve so the ignition will advance when the idle drops.

You don’t get much of an idle drop with the electric AC so I haven’t had to bother with anything like this.

Already tried various combinations. Motor just gets into an oscillation mode even with a 2 degree advance.
Thanks for the suggestion.
Johan

[Jonny H]

Originally Posted by Uwon

Already tried various combinations. Motor just gets into an oscillation mode even with a 2 degree advance.
Thanks for the suggestion.
Johan

I guess you don’t have an input on the ECU to apply additional advance either?

[Speedy Squirrel]

You didn't elaborate too much on what you did previously to implement the Tech3R IAC based AC control, so sorry if this redundant:

1. Make certain that you don't have any vacuum leaks. A large leak can use up a lot of the rotary idle control valves range.
2. Make sure the rotary idle control actuator is not hooked up backwards using the Tech3R actuator test capability. It should open with increasing duty cycle.
3. Using the Tech3R actuator test capability, establish the minimum and maximum pulsewidth. Do this by observing the pulsewidth below which the actuator does not close any further, and above which the actuator does not open any further.
4. When FULLY warm, the engine should be able to idle with the rotary idle air controller disconnected. If not, use the idle adjustment screw sticking out the side of the throttle body to achieve idle. In very rare cases, it may be necessary to drill a hole in the throttle plate to achieve a good idle.

Now you have the full range of the rotary idle controller to use with the Tech3R idle AC table. This is more than enough to compensate for any AC load.


Also keep in mind that, if the spark timing at idle is ridiculously retarded or advanced, you may have problems with the steps above. Somewhere around 5 - 10 degrees of advance at the crank is the right amount.