'83 CIS cold start low idle issue
 

I'm working on a '83 SC that is exhibiting the following symptoms:

To get the engine to start, I am having to open the idle adjustment screw on the throttle body several turns. The engine starts right up but at a low idle - approx 800 rpm. The idle slowly increases as the engine warms up. When the engine is fully warm, the idle is at approximately 1800 rpm. The car runs great, pulls strong and when I turn the idle adjustment screw back in it idles smooth. Hot start is ok.

I've tested the frequency valve - ok
Auxillary Air regulator - has power and closes fully
Cold start circuit working
Power to WUR and pressures are good; 1.5 bar cold and 3.5 bar hot
Compression and leak down are excellent.
Idle drops a little when the oil cap is removed.
Accumulator is good (residual pressures tested and good).

Ive looked through the threads on here and have not seen this discussed.

What I haven't tested is the deceleration valve or axillary air valve. Would either of these cause my problem? Is there a way to test them? I have several of each in my spares. Changing them out will not be easy, though...

Thanks,
JB

Sounds like you have done a lot of diagnostic. How about vacuum leaks. Vacuum is used to pull vapor out of fuel to the filter near the oil tank on the right side.

I think high idle means lean. Low idle may be rich.

Hope that helps.

ST

I meant fuel vapor, not fuel

if you leave the idle screw as it is (hot idle 950), can you cold start the car with cracked throttle? Can you keep it running with throttle at let's say 1500rpm? does it run well? If so, you have not enough air coming in for cold starts.

i spent 1,5yrs troubleshooting the cold start issues on my 81 SC, and eventually i found out that the csv mounting flange was closed (you have an open and a closed part nr. for this flange...the PO obviously mounted the wrong one in my case), which means none of the AAR, decel valve, AAV, works. That whole trombone circuit did nothing. It's a long shot but maybe worth checking out? mind you, it is not fun to check that behind the TB...

I’ll try that today. What you say makes sense as it is acting opposite of what is expected. I have even tried disconnecting the hose/aluminum tube at the AAR and no difference on cold start.
Thanks!

same thing with me: i could disconnect the AAR without any changes in behaviour. It is a very rare problem though, i have found literally 1 thread on the whole of pelicanparts with the same issue.

bottom 2 posts:
http://forums.pelicanparts.com/porsche-911-technical-forum/101814-weird-cis-idle.html

Howdy, ST.

The charcoal canister is the filter I think you are talking about. That system does use vacuum to suck the fuel tank vapors into the engine but the vacuum port is on the left side of the airbox where the air filter is and it's before the air sensor that lifts to meter fuel. Vacuum leaks after the air sensor are what will confuse the system.

It's vacuum from air pulled through the air filter. All of that air has one place to go and that's past the air sensor which turns it into "metered" air for lack of a better term. Air sneaking in past the meter is called false air.

Decel valve can.

http://forums.pelicanparts.com/porsche-911-technical-forum/930615-cis-idle-speed.html

See post 7&8.

A German indy shop wrench just reached in with a set of channel locks and squeezed mine back in 1997. It was idling high and dropped right down.

Plug the little hose with a golf tee first and test. I don't know how to test the actual unit itself but it is doable.

you can bypass the DV by removing the small hose and plugging it.

I would suspect lean as rich would surge at idle plus cold likes to be rich.

start it cold and push up on the air sensor plate and see if the idle comes up or it idles better.

following this thread as I have the exact same problem...low idle at startup, rpms will slowly rise as the car warms up. once warm, runs just fine. Warm start, no problemo.

Subscribed...thanks for posting!

I finally pulled the motor out today as I couldn't remove the csv fitting with the motor installed. Low and behold it had the blocked one installed. Thank you Wreckah for posting and suggesting that this might be the issue. I will update when I get the correct one installed and running.

http://forums.pelicanparts.com/uploa...1549845685.jpg

http://forums.pelicanparts.com/uploa...1549845737.jpg

Another wrong part victim.......
 

JB,

The person who installed your CSV flange failed to notice that the flange was for early CIS engines without AAR. There is a big problem when ordering the CSV flange if you are not aware about the difference.

http://forums.pelicanparts.com/porsche-911-technical-forum/1020014-csv-flange-911-110-264-00-alert.html

If you order using the correct part number, you could still get the wrong part in the package. See above pictures.

Tony

Could this be my problem to? I have it narrowed down to not enough air when cold. I´m gonna check the AAR. (When the weather gets a little warmer, my garage is freezing, no fun wrenching with thick gloves) I´m hoping to find it stuck closed. If not, I know where to go next. (Hoping I dont have to get in behind there).

Mine is a 77s. It has the AAR, so I suppose it should have the open CSV flange?

I'll have to take a look at mine next time i get the motor out... if this turns out to be the problem, im going to punch myself in the face! Because I was the knucklehead that installed a new CSV flange and didnt look to see if it was blocked off!

Cold start valve flange test.........
 

AndreasK,

You could determine the type of CSV flange you have by doing a simple smoke test. A partial engine drop would help get the intake CIS rubber boot (“Pope”) removal much easier with the added overhead space. After you successfully remove the “Pope boot”, plug the throttle body with a latex glove, plug the rubber vacuum hose going to the oil tank with a rubber stopper, and leave the vacuum hose to the AAV unplug.

Inject air or smoke into the air box:
a). If you have the “open” CSV flange, smoke will be coming out from the unplugged vacuum hose going to AAV.
b). If you have the wrong flange, no smoke will be observed from this unplugged vacuum hose.

Or you might find some unsuspected places producing air leak/s. Keep us posted.

Tony

Thanks Tony! Excellent description. Even I understood all of it :) Just waiting for a bit of warmer weather and I´ll be going in there. I´m hoping for a stuck (closed) AAR valve.

happy i could help for once! :)

i just drilled mine carefully and refitted it...

I just bought and installed a new replacement CSV fitting from Our Heavenly Host. I cant remember if I verified if there was a hole or not. Off I go to check it and drill it if necessary...

Thanks for posting this as it could have saved me a lot of frustration!

Maybe this problem is more common than expected. My AAR works as intended, apparently. Open when cold. Closes fully after a minute or two. Won´t idle when cold, without feathering the throttle. With throttle I can keep it steady around 1100 rpm. Idles by itself around 950 after a minute, but hunting slightly, while warming up. Steady idle 950 when warm. I suppose its running slightly rich until warm. Runs great when warm. Tony´s smoke test next. Has anyone removed the CSV flange without dropping the engine? Or am I best of waiting until I at one point do drop it? I haven’t, at the time, got any other reason to drop it, and I can live with the car running as is for a while.

i removed and drilled the csv flange without drop. It is NOT fun :)

Sweet. It´l depend on my mood towards spring then :D

I did a partial drop (lowered the rear of the engine a few inches) and got the CSV flange loose but the hose attached to it was so stiff, I couldn't get it loose. After all that work, I ended up dropping the motor anyway. So much easier, especially the CSV install with motor removed. Incidentally, when I got everything back together, the decel valve was not working properly producing a continuous high idle. Unplugging the vacuum hose (and plugging it) brought everything back to a nice idle. My take is you don't need the decel valve anyway.

Incidentally, I have found 3 CSV flanges in my spare parts jungle and they were all the closed variety even though the systems they came from were later US or Euro CIS. Makes you wonder...

Decel valve delete.........
 

JB,

You could remove the decel valve if is defective or leaking. But you need a good working DV. People who removed it does not understand how a good working DV plays an important role in the operation of CIS. If you strongly believe that there is no need for a DV in your engine and would make you happy, nobody could stop you from doing so. It is your car and not ours. And I won’t do it for my engines. The lack of understanding and knowledge is difficult to overcome. Keep us posted.

Tony

Tony,

Lack of understanding and knowledge is not difficult to overcome if someone such as yourself is willing to explain it to someone interested in learning.
Please enlighten me as I am always interested in learning.

Jim