Engine idle drops with A/C
 

Hi All

I noticed a strange problem when I operate my air conditioning in the car.
When I operate it, the engine idle drops. it even worse when the head lights are on.
I know that there should be some vacuum unit that controls the idle level but I dont know where it is...or maybe the problem is somewhere else? :confused:

Can somebody help me with this issue?

Thanks.

A/C units area huge bog on the engine. This is why you get better gas mileage with it off. There are lots of vac units behind the HVAC controls if you want to know where they are. You should only hear them woosh when they move a lever, but should stop after that. If it's continuous vacuum noise, then you probably got a leak.

Thanks, the units should physically move the throttle a little bit? or they just "pump" air into the engine to make the idle higher?
Those vacuum units are in the engine area? or inside the car?

Depending on the year of your car, there's most likely a valve that's designed to allow more air to the intake when the AC is turned on, thereby increasing idle speed and avoiding the drop you speak of. My 78 does not have one but most cars I've seen do have the valve and hoses attached to the crossbar. I'm really not familiar with troubleshooting them though. It would help if you'd give some details about the year of your car.

As for the idle dropping when the headlights are on, this could probably be solved by cleaning the electrical connections at the battery, starter and jump post as well as your ground points.

Yes, Stephen is correct. I forgot about the piece that hangs from the crossbar. Yes, this is a switch that opens (air) to increase the idle higher when the A/C is kicked on. You could probably test that this is getting voltage when the A/C is on and off. Those HVAC vacuum solenoids are in the center console. Also probably depending on what year. I have an OB so that's where mine are.

What year is your car?

The later cars have a signal feed to the LH ecu that tells it when the AC compressor is engaged and compensates the idle. Its one of the standard actuator tests for the ecu diagnostics devices (Bosch Hammer or equivalent)

I am sorry, the car is from 1980.
Is there a way to check this unit that hangs of the crossbar? or the only check is to see if it gets 12V when opening the A/C?

Check for 12v when its supposed to be working, and you could also pinch one of the hoses either coming or going from it to see if the idle speed changes when its supposed to be open.

Thanks, I will try to check in the following days!

Was that electric air valve retrofitted to some older cars?

My 79 doesn't have it, but I have seen pictures of 78/79's with the valve.

Some early and Euro cars didn't have factory AC.

Do you have a couple wires unattached from the front harness?

Maybe check PET6?

Hey Raymond,

If you feel left out by not having one of those hanging from your crossbar, I can make one out Bondo and Silver Paint it and a couple wires and presto! SmileWavy

That's odd because my car has factory AC, yet no valve and no sign on the crossbar that a valve was ever mounted there or any unexplained wires. Keep in mind I've never actually gotten the AC to work and that the compressor and hoses are now in a box in the garage.

The aluminum crossbar I got off of ebay did come with a valve but I may have thrown it out.

Only if it has some kind of vortex generator built into it so that improve power and gas mileage! :D

No evidence of my car ever having had one, no loose wires.

Wonder if it wasn't specific or added on to cars with auto trans in order to help them idle in gear with the A/C on?

Can you (or anybody) please tell me if this valve has a Porsche part number? mine is very weird (no numbers) and doesnt do anything so I thought of buying a new one...I still don't understand if this is something that was originally made or was added later :confused:

I am sure 928 Intl would have a good used one with a warranty. Or you can get a 2nd mortgage on the house and buy new.

Dont want to take a 2nd mortgage :(... I didnt find this part in their web site...do you know the part's name?

928-606-215-01 $111 for the Porsche part here on Pelican.

Thanks!

Mike is a PET Guru!

Also, where are you located. It would be best to just swap with a know working one so your not wasting your $$

If this valve is also used in other cars then this is what I will do...just buy something similar since I dont live in the US and it does cost a lot with the shipment...

Fill in your profile with your location.

Done :)

Its a 12v about half inch passage air valve. My guess is that any aux air valve that opens with 12v should work.

Well, I have some interesting findings...

The valve that i have now is working. the default position is closed and when there are 12V it is open.
The interesting part is that when I disconnect the hose from the valve (the output hose), close it with my finder and then start to remove the finger while the engine is working - the idle starting to drop instead of rise!!! :confused:

Does it mean that I have a poor fuel mixture? I have to much air in the system so when I put more air the engine cant hold the idle?

Does it mean that I have to adjust the "CO bolt" so the engine will get more fuel and then when the air valve will be opened the idle will rise?

Or should I do something else? :confused:

Air through the Aux Air valve should come from the same place as air for the throttle comes and goes to, which is metered air. Since you used your finger, I am assuming the source was NOT metered air, try it hooked up correctly.

Unmetered means the air did not pass through the air metering device below the air filter. If it doesn't go through, no fuel is added to compensate for the flow, and no "adjustment" will really fix it, just hook it up correctly.

Well, when it is connected correctly, the idle also drops...I tried to connect it directly to the hose from the air meter (bypass the air valve) but the idle droped even more.

Maybe the air valve - that is NOT original, lets too much air to go through it?

Its really confusing...

Maybe you have a serious vacuum leak(s)?

Are you comparing having the valve connected vs leaving the hoses open to the air?

Post some pictures if you can, but I suspect some things are not hooked up correctly.

Yes, this is what I did.
I compared between those 2 cases.

The "output" hose that goes to the engine has a strong vacum but the input hose that comes from the air meter under the air filter seems to be neutral (?). I assume that the output hose "takes" only the amount of air that the input hose provides (according to the air meter)
I didnt see any air or vacum leaks but in the weekend, I will look under the air filter as well...
I will try to upload some picture during the weekend becasue I am busy until then

funny problem...

Only air that passes through the air meter has fuel added for it.

Any connection below the throttle plate in the throttle body should be "neutral" pressure metered air.

The Aux air valve goes from the base U below the throttle to a port above the throttle. When the valve is open is should be exactly the same as slightly pressing the accelerator to open the throttle.

My guess is that you have some "creative" plumbing, with hoses going where they should not go.

electric air valve
 

My 78 doesnt have this "electric air valve" from the crossbar either, and it does have A/C

http://forums.pelicanparts.com/uploa...1243985495.jpg
http://forums.pelicanparts.com/uploa...1243985509.jpg

I think that tomorrow I will upload some pictures of my plumbing...
There is so much "creativity" in that car that was done by the previous owner that it just makes me sick.

We all wonder why these cars were put to so much torture. It's literally mind boggling to see such workmanship being abused.

Yeah, post pics as they are worth a 1000 words.

Yeah, same with Raymonds (rjm65) 79. I did tell him I had some spare pieces of wood lying around and I could Dremel up one if he felt out of place. Same offer applies.

I though of something...can someone post some pictures of that air valve area so I will be able too see the hoses connections.
I want to see the input hose origin area and the output hose...
I will post my pictures tomorrow

On my US 83 the Aux hoses are very simple.

Hose from the front of the intake "body" goes to the Aux valve.
Hose from the Aux valve goes to a Y fitting.
One hose from the Y fitting goes below the base of the throttle body.
Other hose from the Y fitting goes to the carbon canister vent flow valve on the fender.

One thing to remember about this guy's car is that it is CIS.

Yoni, if you pull a vacuum line and your car loses idle speed, then it is getting too much air and probably running lean. There is not enough information for us to tell you whether you need to adjust your idle mixture, which is what that screw actually does. In fact, your car might be running perfectly.

M '85 S2 has LH injection, but it also has this vacuum valve. I think it makes a tiny "click" when it comes on with the AC compressor, and the idle stays dead even. This part is your culprit. Have you tried spraying some WD-40 into it?

Good luck. pix will help.

N

Hi!

I am sorry but I dont know what you mean by CIS...
This vacum part is working perfectly. it makes the click and it becomes open when I turn on my A/C.
Maybe it puts too much air through it since it is NOT an original part.
Anyway, I am uploading some pictures...maybe it will help.


http://forums.pelicanparts.com/uploa...1244223806.jpg
http://forums.pelicanparts.com/uploa...1244223887.jpg
http://forums.pelicanparts.com/uploa...1244223956.jpg