81 SC Almost Stalls At Stops
 

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!

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

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 ..

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

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.

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

Thanks all. I'm a little cornfused. This is the decel valve right?
http://forums.pelicanparts.com/uploa...1379459156.jpg
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!

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

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:

http://forums.pelicanparts.com/uploa...1379515536.jpg

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

http://forums.pelicanparts.com/uploa...1379519260.jpg

- Manfred

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.

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.

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?

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

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

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.

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?

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

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.

Decel valve isolation........
 

Ernie,

Is your '81 SC a USA or Row model? The USA late SC models have a different decel valve than the ('76-'79) 'red decel valve' posted. Unless you have a RoW car, the decel valve would be similar. Removing and plugging the vacuum hose from the top of the decel valve would isolate it (decel valve) and do nothing as you suggested would work only if:
a). The by-pass valve inside the DV (decel valve) is at closed (sealed) position.
b). The diaphragm is good and not leaking air/vac.

Otherwise, you just plugged a leak source by plugging the vacuum hose with a tee and allowing a vacuum leak source (decel valve).

Tony

Tony I have had my car for thirteen years and have not been curious about row vs US up until a few days ago when I seen the "zzz" for vin. I will check ins papers tomorrow car is put up and I just had ankle operation. Anyway my valve is just like the red one not a pancake type. I had the same issues for years and sealed the hose this past summer. No more high or low idle at stop. I am open to any info you can provide. Also is the "zzz " the one sure way to tell if it is a row or not. I do not have the fender side lights
Thanks Ernie

Lambda/ECU........
 

Ernie,

Do you have an OXS sensor or ECU (lambda)? Euro or RoW SC cars don't use an ECU or OXS. Could you PM me the serial #? I could look at my reference booklet. Thanks.

Tony

That kind of stalling can also be an indicator of an over rich air fuel ration...when was the last time your co was checked/set?
BTW, I have a 930-10 euro motor in my US spec and vin car....I swapped out the US 930-16 for more HP and a fresh engine.
I have the decal valve like the pic shows not the US type.
What are your engine numbers, easy to tell.

Thanks everyone. I'll try plugging the vacuum line to the decel valve. I have a US-Calif 911SC. My decel valve is like the photo that ManniB posted NOT the pic with the red Euro one I posted. I was cornfused, but clarified with the help of Pelicans.

If I have a bad Decel valve, I will probably replace it, as I have to smog my car every two years.

I recently had my car's CIS system gone over before this started, and they did adjust my mixture using a CO meter.

If this issue started after that adjustment I'd have it verified elsewhere....if the machine hadn't been calibrated lately they can be way off....I went to two well respected indy shops on the same day for a check (both excellent actually) and the dif between the older machine and the new computer deal was 1.2 CO...that is a huge difference.
My car was doing the same after the first setting when cold...stop and die, when warm it would almost die...it was just too rich.
Since then I put an onboard AFR guage so I can now set it myself.

My motor looks like this, where is this small diameter hose I should plug? Near the front or back? I tried to locate it really quick before work but couldn't find it so easily. Wondering if previous owner got rid of it already...

Tested removing the oil cap during the warm up and it seemed to have affected nothing

I have had this in the past. I would call it dangerous in that it helped me get into a nice rear end collision. Coming to stop, engine started to stall/warning lights on, glanced down for a split second and boom - whacked the Jeep Cherokee in front me that stopped abruptly...Really my fault but I believe this helped me do a number on my front end by distracting me at the worst time.

You said you just had your CIS gone over and they set the mix.....I have had it come back from shops like this with mix freshly set. Some shops just dont care too much about driveability. I believe in these cases the mix was too rich as slighlty leaner settings later on alleviated it. Also bumping up the idle myself from 800 or so to 950 (leaner idle) helped the rpms not dip so severely upon coming off the throttle. I have heard timing can also play into it as well.

I would check mix, idle speed and timing probably in that order. I think a well functioning Decel valve could also help - and on paper is probably the quick answer - but may not be the only answer here depending on what settings you are running.

As a note, I have, at times, run my car with the decel valve disconnected, but with the mix/idle set at spec., had no decel stalling issues even with AC and lights turned on.

I have a feeling you are a tad rich on the mix as a result of whoever just set it.

Took my car to a shop, and the mechanic popped off the airbox cover and removed the air filter and adjusted the mixture. Yes, it was a tad rich. It runs great now.