CIS warm idle goes lean

[L8apex32]

My 1981 SC euro starts fine, warms up well, then has trouble idling. It doesn't seem to idle at a high rpm when cold, but it does idle solidly at maybe 1200. I can drive it and even race it with no trouble. The main problem is warm idle. It seems to want to idle between 1200 and 1000 rpm, but goes too lean when warm. Here is what I have done to troubleshoot, maybe you can help.

The way I know it goes lean at warm idle is because, once it starts running rough after warm up, I can lift the air sensor plate just a little and it smooths out the idle.

System pressure is 5.2 bar and control pressure, after warm up, is 3.0 bar. [I set system pressure to 5.1 bar in the summer and reading it now, in the cold, its 5.2, fyi.]

My WUR is the Bosch model ending in 089 (its a Euro). If anyone has the full specs on that WUR and would share them, I'd be appreciative. I can't find the full specs for the Euro engine components.

As far as false air, when I take off the oil cap, it definitely reduces the idle and makes it idle worse. I've had the system checked for air leaks this summer and the ones we found, we fixed. I am somewhat sure I don't have false air.

I can use the throttle to increase the rpms, and that works and it will run at elevated RPMs just fine.

I tried increasing the idle richness when warm, but its not like it needs just a small turn or two. It would take many turns and that would make cold start way too rich. At least, that is my experience so far.

The AAR is a throttle bypass, but not an air flow sensor bypass. It doesn't mess with mixture. So, it shouldn't have an affect on this issue, right?

The cold start valve is listed as a possible problem, it could leak, but that would increase richness, not decrease it.

The WUR we can check exactly, if we have the exact specs for the 089.

Because my car is a Euro, it has no O2/Lambda system. It has no cabin heat, either. Seems like other recent posts on this issue may have been caused by one of those features.

I am hoping that others on this list have some ideas.

[Paulporsche]

Those pressures sound OK. What is your cold control pressure?

What is your CO% set at?

The AAR raises the idle @ startup, but yours may not be opening enough. Also, my engine has no lambda system so it actually can have varying cold start speeds, depending on the ambient temperature. Where are you located?

[Bob Kontak]

[boyt911sc]

Check your cold control fuel pressure versus engine rpm until the engine rpm settles down (stabilized). Meaning data from stone cold engine to 4 or 5 mins. run. This would all depends on your location so include ambient temperature.

At this time of the year, your car would give a different reading when you start it in Montreal or in Miami. By just reading your post, I tend to suspect your cold setting. Even if you are located in AZ, your cold start RPM (early AM) is rather low. So without a systematic test and inspection, all these are speculation or guesses.

Hook up a fuel gauge and start collecting data points. BTW, how did you check for vacuum leak/s? Spraying starting fluid? Keep us posted.

Tony

[timmy2]

From your description, it sounds like you are getting some false air once the car is warmed up.
Make sure your AAR is closing when warm. (Yes, it can affect mixture as it supplies air directly to the throttle body below the throttle plate beside the Cold Start Injector) Here's a quick test for the AAR:
Pull it, put in the freezer for 1/2 hour to open it fully. Then hook up 12 volts to it and see that it closes fully within 3-5 minutes depending on type.

Also/alternatively as you have an '81, try disconnecting the vacuum line from the decel valve and plug the line. Cap the nipple as well. See how it runs. they can fail and cause idle troubles.

Your AAV can also fail and continue to supply false air. It is supposed to close by vacuum after an initial "burst" of air to help in starting the car. (Test by applying vacuum, tough to do with engine in the car.)

If all devices are working normally, Then do what Tony has suggested.
http://jimsbasementworkshop.com/CIS/CIShome.html
http://www.auto-solve.com/mech_inj.htm


Decel valve is the gold disc with the vacuum fitting in the middle of it:
(Picture courtesy of Jim's Basement CIS Primer)

[T77911S]

according to bob's chart, you should have 3.6bar warm WITH VACUUM. without vacuum it should 2.9bar. you have 3.0 warm and running(with vacuum).

you also need to check the cold pressure. this relationship between cold and warm is what is important. when WUR's go bad, the difference between to the two gets less and less.

it could be your WCP(warm control pressure) is too low, due to a vacuum problem, and perhaps the mixture has been adjusted and now you cant get a good balance between cold and warm.

5.2 to 5.1, i would not have messed with it.

make sure the AAR is working.

[Vereeken]

The system pressure is ok.

The warm control pressure is too low. And it is too low by 0.5/0.6 bar which is exactly what is added in pressure by the vacuum assist to the WUR.

So either the left side vacuum connection is not connected to the 089 WUR, or the thermal valve (incorrectly called Thermo Time valve in my drawing) does not open anymore.
Or the vac attachment at the throttle body is not correct (you can inadvertently swap the vac connection of the distributor and WUR). it is easy the vac line to WUR should have vac at every rpm the vac to the wur should see vac pull increase by increasing rpm.

It is also possible that the decel valve is bust and this would allow to let air in after the throtlle butterfly which can screw up the AFR.

The decel valve on a EURO SC is NOT the decel valve shown by Timmy 2. We euro owners have another type of decel valve to the left of teh air filter behind the throttle body. There should be a T connection with vac lines coming out at the top.

I have found that 1 in 2 of these type of decel valves are kaput. Some have small tears in the diapraghm, others have no diaphragm left anymore. They are a POS.

Check the pressures again and also state the outside temps.

Also check the vac connections...see my drawing attached. You can not use teh US diagrams to solve this.

Michel

[L8apex32]

Thank you all so much for the help and advice. Here are the answers to the questions I have at this time:

I do not know my CO% or any other exhaust gas measurements. I don't have those tools.

I'm in Kansas City and it was between 40 and 50deg F.

Thanks for the documentation Bob Kontak. That is just what I needed.

The next time I start it up, I will record control pressures from cold start all the way until it levels out/maximizes.

We checked for vacuum leaks this summer using two methods. 1st was by spraying brake cleaner on and around the intake. That found a few. Next, a shop in town has a smoke tester. That is one cool system and worked great. It found another leak or two that we fixed.

I will try the AAR test - checking it cold and then with 12v applied.

I am not sure what the AAV is or what it does.

My WUR does not have the vacuum line attached, as Vereeken deduced. However, I might misunderstand how it works. I thought that at high throttle positions, there is less vacuum in the intake manifold and then less vacuum at the WUR and, therefore, richer. This assumes the vacuum line to the WUR goes to a port below the throttle. Your drawing and my understanding match. Is this incorrect?

My distributor vacuum line is also not connected.

I have the decel valve as Vereeken describes. Do you know how to test it?

I think it clear that I don't know what the AAV is and will need to read about it when I get home.

Thanks for the help, one and all.

[Vereeken]

What you are describing in terms of WUR and vac interaction is true for WURs with vac enrichment. The 089 is not one of those.

The vac line to the 089 serves another purpose. It is connected to the TB and between the TB and the WUR you should have a Thermal Valve.
This thermal valve holds off Vac to the WUR for 45 seconds when dead cold. It is heated through a 12v source and not engine heat.
By holding off the vac to the WUR at cold start it allows the WUR to start with a control pressure that is about 0.5 bar lower then with the Vac pulling on it. After about 45 seconds the Thermal valve opens and allows vac to the WUR thus increasing the control presuure and thus leaning out the mixture.

I believe this setup for Euro cars was present to help prevent airbox backfires.

I have not seen any evidence that the vac on a 089 falls away at high revs and high engine loads, thus enrichening the mixture. I do believe that the enrichment on the EUro SC comes from the air funnel shape alone at high revs. But I could be wrong.

So in essensce the 089 vac line is a leaning out feature and not an enrichment feature (which is the case with the 045 or so).

That is why it is important to connect the vac line to the left of the body and connect the nipple atop the 089 to atmosphere or to the appropriate nipple on top of the front TB. the top nipple should not be vacuum assisted.

The 089 is poorly documented and is fairly unknown because it had a short life.

Look at the document from BOb. it says testing vacuum. It means that you have to apply vac to the vac port when settin the control pressure!

The AAV does nohing on a Euro SC. When it works it bypasses air around the throttle plate only at startup so the engine receives a big fresh air intake. If it is kaput too bad. Usually it is a diaphragm that ruptures. But it does not interfere with AFR (unless ofcourse you have a hole to the outside).

The decel valve can not really be checked in situ. You have to take it off. If you can blow through the big vacuum hose connections it is kaput.
It really creates all kind of problems...I have seen most SCs in Euro run with the thing disconnected. As i said I out of 2 is broken.
I like the decel valve because of it function but I am on my third one in maybe 5 years...ofcourse none was new but still...

Michel

[john walker's workshop]

did you ever set the hot idle mixture on an exhaust analyzer? they do go leaner when they warm up.

[timmy2]

Sounds like the decelcalve on your euro is the same as on my '78 euro, the drawings on Jim's basement are correct for my car except for the egr stuff. The factory must not have changed the euro cars like the US cars.

[Vereeken]

To the left the big AAR flying saucer. You can see that the AAR can not affect idle mixture given it pulls air after the throttle sensor plate (bar ofcourse holes in the thing)

To the right in the sun the decel valve on a stock 911 SC EURO.

Pardon my photo shooting skills.

[timmy2]

Looks just like my '78 except for the engine underneath...:

[L8apex32]

A quick check of cold control pressure shows 1.3bar at around 42 deg F. This is with engine off, and no vac hose connected, so no vacuum.

Based on no vacuum (which means lower control pressure readings), I would think the value should be less.

I may not be accurate on temp since I recorded outside air temp, not inside garage temp. I'll re-check and re-post when I have verified.

[Vereeken]

It is a bit outside of the normal operational range.

Ofcourse as you said if it is 42 outside what was it inside because that is what counts.

[T77911S]

it should be less.

vacuum on the WUR is actually called WOT enrichment. but i figure as you have, porsche added the TTV for cold starts to protect the air box.

you can pull a vacuum on the WUR and see where the diaphragm pulls in an out. then you could monitor vacuum while driving and see when it drops to that level. and/or you can record the CO and see when it goes rich, but, the AFM is also shaped to go rich in the upper RPM's too. perhaps a test without vacuum to the WUR to see where the AFM richens it up.

i have done most of this, i just did not have the tach adapter to tell what RPM some ofthis happens....until now. now i dont have a car.

[L8apex32]

Here are the numbers for my WUR (089), 49deg F, no vacuum connection, engine not running (fuel pump relay jumped, ignition on):
seconds pressure
0 1.0-1.4 bar (oscillates)
9 1.4 (stabilized rest of way)
21 1.6
60 1.95
76 2.1
90 2.2
120 2.45
150 2.65
180 2.85
210 2.95
240 3.0

I have removed my AAR to test it. Bosch 0 280 140 201. It was 1/4 open, give or take, at 49 deg F. After 12v was applied, it slowly closed over a few minutes. Its now in the freezer to see if it opens more than 1/4.

I removed my decel valve. Its Bosch 0 280 160 111. I can not suck air through it nor blow air through it.

[john walker's workshop]

you didn't answer my question yet.

[Vereeken]

Those numbers look close enough to me.

I do not know why the pressure would oscillate with the engine off. I have never encountered that. I have had a 089 with a ruptured vac diapraghm but you could not have tested taht with the engine not running.

So what is the total pressure when the vacuum line is attached the engine is hot and running.

As far as I can see from here AAR is also fine.

So the warm idle problem must be a mixture or vacuum leak problem.

At this point in time we would need an exhaust gas analyzer or AFM like an LM 1 or 2.

I think we will see a very lean AFmixture when hot.

[Vereeken]

Originally Posted by john walker's workshop

you didn't answer my question yet.

In a way he did. He said he did not have access to these tools ;o)

But indeed at this point that is what needs too be done first.

MOst likely he has a vac leak somewhere.