81 SC Almost Stalls At Stops

[aoncurly]

Hi Everyone,

I am having a problem with my 81 SC when I clutch at a stop. When braking for a stop, I clutch, the engine revs will drop to almost 0 and the alternator light will light for an instant, then it returns to a normal idle at around 850 RPM. This just started. Happens every time I stop, warm or cold. Clutching between shifts seems normal.

Any ideas what could be wrong?

Thanks in advance!

[timmy2]

Check your decel valve vacuum lines if your car has one.

[theiceman]

when my car did this i discoverd that the actual idle adjustment screw had moved.. pretty strange i know .. i wanted o fix it remporarily so thought i would boost the idle a little.. i went to turn it and went allmost a full turn without the idle even moving .. i decided to just leave it just before the idle started to go up and it cured the problenm .. been about 6 months now .. i founds it relly easy to turn so figured the spring was just really weak and it backed out.
I hope its something simple like this ias the decel valve is round back and thats a pain ..

[aoncurly]

Thanks for the replies. Will check my vacuum lines to my decel valve.

[Bob Kontak]

Originally Posted by theiceman

when my car did this i discoverd that the actual idle adjustment screw had moved.. pretty strange i know .. i wanted o fix it remporarily so thought i would boost the idle a little.. i went to turn it and went allmost a full turn without the idle even moving .. i decided to just leave it just before the idle started to go up and it cured the problenm .. been about 6 months now .. i founds it relly easy to turn so figured the spring was just really weak and it backed out.
I hope its something simple like this ias the decel valve is round back and thats a pain ..

Decel valve on the 78 and 81 are different looking parts. The 81 is on the passengenr side and you can pull a small diameter hose off easily to check vacuum. The aux air device is set back a little further and it has fatter hoses on it.

There may be something to the idle air bypass screw you mention. aoncurly should try taking his warm idle up to 900/950 vs 850. Unscrew to increase idle. It is the dime sized fat screw on the drivers side of the TB. Easy to move.

[emac]

81 decel is just where Bob said. Mine is just right ( about a foot ) of gas filter. It's round disk shaped. Leave it connected to the car but pull the smaller hose off and in my case put a screw in it. Kick your idle up to about 950 and your problems will be over

Ernie 81 sc

[aoncurly]

Thanks all. I'm a little cornfused. This is the decel valve right?

And I'm pretty sure on my 81SC it is on the drivers' side.

When you guys say to check the vacuum line, what do you mean exactly?

I may have been a little off on the idle, but will double-check. It is around 850-950.

Thanks again for the help!

[timmy2]

Is your car a ROW?
The US versions have a decel valve that is mounted near the #6 intake runner. If your car has a decel valve as pictured it may just need adjustment

[aoncurly]

My 81SC is a US (California) car. I noticed a some fraying of the small hose that leads to the decel valve, but do I just disconnect it and if my car still almost stalls at stops, it is the hose? I'll replace it either way. How is the decel valve adjusted? Here is a pic showing my decel valve:

[emac]

That is not it. It is drivers side to the right of gas filter close to firewall. Pull top hose off and plug. I will try to get a photo. Google photo of it
Ernie 81 sc

[ManniB]

- Manfred

[sigep174]

I have an '80 and this was a problem for me some time back. Turns out I had a crack in my air box. Once that was replaced it solved the problem. I will say I hope it isn't that for you. It is an engine drop to replace the air box.

[timmy2]

Your picture shows the WUR in the box. The picture posted by ManniB should be correct for your car.
Google Jim's CIS primer for good drawings and explanations of the devices on your engine.

[aoncurly]

After looking at the vacuum line at the decel valve (thanks Mannfred), I decided to take it in and have a shop take a look. That line ducks under my airbox and ends up who-knows-where. Set up an appointment, fired up my 911SC and lo and behold, my engine ran great. No more almost stalling when clutching. Stopped my car. Called up my shop and cancelled my appointment. Fired car back up to put in garage, and WTF, I clutch and it almost stalls again.

I decided to try Bob's suggestion and adjust the idle as it was a little low (around 850 RPM warm). I noted the original location of the idle adjustment screw, and adjusted the idle and it seemed to help. It was a little high at around 1100 RPM, so turned back the idle to around 950 or so, ran ok, but noticed the idle creeped back up to 1100. After fiddling with this and getting the idle around 950, I noticed I am just about back to the original location of the idle adjustment screw. Car seemed to run ok, but I am guessing the next time I fire it up it might start the almost stalling-thing again.

Any thoughts from some CIS experts?

[emac]

Have you clamped off the small vacuum on the decel line yet. I still feel this is your issue

[Vereeken]

Originally Posted by aoncurly

Thanks all. I'm a little cornfused. This is the decel valve right?

And I'm pretty sure on my 81SC it is on the drivers' side.

When you guys say to check the vacuum line, what do you mean exactly?

I may have been a little off on the idle, but will double-check. It is around 850-950.

Thanks again for the help!

This is the one found on most Euro SC's.

If you have a true US car it will be the photo posted by ManniB.

They all go kaput. If it is now and then high likely the membrame or spring inside sticks or is ruptured.

The quick test is to drive at high load (say 70mph in 4th) and drop the clutch.If the revs come down easy instead of falling like a brick the decel is ok (but it can be still kaput if it is a sticky spring or membrame but then it will work once i an while).

Michel

[jpnovak]

If you are seeing the idle rpm fluctuate that much then you have issues with timing. Could be a worn spring or possibly the vacuum advance/retard pods are having problems.

[aoncurly]

Originally Posted by emac

Have you clamped off the small vacuum on the decel line yet. I still feel this is your issue

If I plug or clamp the hose, what exactly am I looking for? Will I expect my idle to almost stall when clutching at a stop?

[emac]

On the diagram of the red valve just above, place a golf tee or large screw in the hose that connects to the top of the valve. Do nothing more, no need to to remove the valve. I have the exact valve in my. 81. I feel this will cure your issue.
Ernie 81sc

[tirwin]

What emac said. The decel valve isn't really necessary. A lot of people plug the vac line (and the valve side too). The reason is because the decel valve is mainly an emissions related thing. If you plug it you get better throttle response. If that cures your problem, you can just leave it that way. The valve has a diaphragm in it that eventually fails. That's the most likely culprit.