Engine idle drops with A/C

[MPDano]

A used one is only $40 at 928 Intl and new one is $95. This is OEM Porsche

Part # 928 606 215 01

[Normy]

Yani- look at the picture that MPDano posted. The cross bar, to the left has an object hanging from it with two purple vacuum hoses attached. That is what you need.

Someone applied a little bit of "home technology" and mounted an aftermarket....or well...something to your engine. I bet this part can't work as efficiently as the real part, and that's your problem.

Good luck!

N

[Danglerb]

The device in your last picture is the early style of idle stabilizer valve, and normally they are mounted behind the throttle body, all the hoses coming in going are new to me. Please take a couple more pictures showing where all of those hoses hook up, some close shots, but also a bit farther back to put them all in context.

CIS means early non electronic fuel injection. Your injectors open and close due to fuel pressure vs manifold vacuum, with the differential pressure controlling the rate of flow, and flow generally being "continuous while the motor is running".

[Yoni_d]

Normy - From what I saw, the only difference in that area is that I have an early idle stabilizer instead of the original part...I cant see clearly in the pictures of MPDano how it should be but I assume that the hoses connections are the same...
Danglerb - what is the difference in operation between the two?
I will put some more pictures anyway..but if someone has some close up pictures of that area, it will also help me!

Today I have noticed something else as well. Any electric device that I open - such as head lights makes the engine idle to drop even when the electric radiator fan starts to work the idle drops.
Maybe there is some bigger issue then this valve that causing this idle problem?

I don't know...maybe its all related.

[Danglerb]

Alternator load on the engine changes as the load on the alternator changes, but the Aux valve only uses a tiny amount of power, and when my fan turns on I don't see an idle drop, so I suspect more lurking problems.

Actually I don't think your car is supposed to have one of the active (electrically powered from the brain you don't have) idle stabilizer type things. Without your model year in your sig I tend to not be able to keep track of who has which.

[Yoni_d]

Well, I think that next week I will check all sensor using the manual that I have...
When I start the engine, the idle are about 600 and then after 2 seconds it is rises to about 1000 RPM automatically (when engine is cold). that means that the AUX air regulater does work...I dont know if in a good way but It works.

My car is from 1980 and the origin country is Germany.

I posted some more pictures...maybe it will help.

[MPDano]

Yup, that's exactly what the AAV (Aux Valve) does. One less thing to worry about. But it does drop back down after engine warms up.

[Yoni_d]

But in my case the idle drops right after a few seconds(10-20) and then they are a little low. Is that normal? or should I check something?

[Danglerb]

Everything on those odd looking hoses hooked up to number 5 I wonder about. One port of the non Porsche brown valve also looks open?

http://www.***********.com/model/928-78-82/107-10.htm

[Yoni_d]

Hi..

According to the schema that you attached it is looks odd but according to "MPDano" posted pictures it looks almost the same except that I dont see in his pictures where the output hose from the air valve goes too

MPDano if you are seeing this can you please make some more pictures

There is indeed one more port but it is a sealed one and there are no air leaks.
The thing is that this A/C air valve bypasses the auxiliary air valve. therefore, it should add more air to the air that the auxiliary air valve allows.
I have disconnected the A/C air valve, then closed the input air hose to the A/C valve. With me finger closed the output hose in order the simulate the valve operation.
Then, I opened my A/C and gently removed my finger from the output hose. There was a strong vacuum from that hose (normal) but removing my finger in any case didnt raise the idle...the idle only drop

I think I will have to go and check my CO levels to see maybe I have lean fule / air mixture...

This issue drives me mad!!!!!

[Yoni_d]

I have noticed something that might be interesting...

I just looked at the attached schema which is for 83-86 models and there the hoses looks more like what I have.
The difference between the methods is due to a different type of the auxiliary air regulator...as seen in the red circle...maybe the previous owner combined between the 2 worlds

I want to cry...

[Danglerb]

I believe the devices are the same in the two diagrams, 5 and 20, but you might be right that some previous owner made some creative plumbing. Hoses are often expensive to replace, so something handy might have been substituted for some expensive Porsche hose.

What I think we need to know is where all of the present hoses connect.

Your diagram is I think for Ljet electronic injection, and your car is not, its kjet non electronic injection.

Please put your model year in your profile or sig, I don't want to get it confused with one of the other cars and model years.

[Yoni_d]

I have added the information to my profile signature. My model is 928S from 1980 European.
I think that my hoses connections are good without any modification excapt using not original hoses. but the plumbing it self looks like in MPDano pictures...
I also almost 100% sure that I have electronic ignition since from the distributer I have 2 or 3 electric wires that are coming out of it...but I will make sure again.

I will try to make an exact scema of the hoses during the weekend.

[Danglerb]

Ignition is electronic, fuel injection is not electronic on your model.

[MPDano]

Yeah, DanglerB is correct. You can see on your pics that your injectors are CIS (non-electronic).

[Yoni_d]

Yep it was my mistake since I thought he was talking about the ignition...sorry about that...

[MPDano]

Originally Posted by Yoni_d

Yep it was my mistake since I thought he was talking about the ignition...sorry about that...

NO worries as I did the same exact thing. When someone says Distributor, I automatically think Ignition Distributor. I never heard of CIS until I bought my Euro.

[Danglerb]

Engine speed is pretty much how much air gets to the cylinders. More air and it speeds up.

Air / fuel ratio, the mixture rich or lean, will effect the engine rpm to a lesser extent, but a mixture that is more than a little off is going to make the motor, miss or stop running. What I am saying here is that added air is very unlikely to decrease the rpm even if it messes up the air fuel ratio.

I suspect that something we haven't found yet is the root cause.

[Yoni_d]

I that case, what do you think? what things do I have to check and how? (beside making sure that the plumbing is ok)

[Mrmerlin]

that brown switching valve is from the 944 turbo .
It bolts under the 944 intake manifold