High Idle - CIS issue
 

I have been having a problem with my 1980 SC. When cold, it starts up, but only idles at around 600 RPM, and sounds like it's going to stall. After driving it down the block, it settles into an idle of around 1100. Once warm the idle goes up to about 1250, and stays there. I have tried adjusting the idle screw until it is closed, but still can't get it to go below 1200-1250 RPM.

I have checked for vacuum leaks, using carb cleaner on the intake boots, vacuum hoses, the airbox and fuel injectors. I have also examined the AAR when cold, and it is opened, and when warm, it looks to be closed.

One thing I was told, is that the Vacuum housing on the distributor may be no good, but would that not allow me to adjust my idle?

Where else should I be looking, and what other tests can I perform?

Thanks

barring that you don't have any vacuum leaks that you know of, yes the distributor advance/retard weights could be stuck. You can test the retard easily by sucking on the line, the advance though us not as easy, it'e very hard to see it move. The best way to insure the advance s free is that the rotor when twisted should "spring" back into position.

According to PET you should have a vac limiter fitted, you can adjust your idle from there. Loosen the lock nut, loosen the hoseclip a bit, screw the rod down and see if it makes a difference. Stop when you get to where you want. You are going to have to open that idle screw a little bit if you haven't just left it where it was.

The vac limiter is the bit with the hose coming off the top of it. It tees into the thermo valve and the throttle body - spot the connection.

http://img.photobucket.com/albums/v2...Rwork065-1.jpg

Isn't that the decel valve? It controls the rpm's from dropping to fast.

Call it that if you want - my mechanic calls it something else too. On Renault K-jet we called it a vacuum limiter.

Whatever you call it, it vacuum-assists the revs, so try adjusting it if you have it fitted.

80's don't have that, first year for the frequency valve.

2nd on the Deccel valve.

Check your vac routing again. Pelican has the diagram online for FI 911SC. It's critical especially to that electric switch on the heater fan mount.

If you're sure that everything is right then the only other thing I can think of is the intake runner injector seals. Not the ones with the rubber O rings on the injectors themselves but the ones that hold a seal to the runner to phenolic tube that the injector slips into and is held in by the fat o ring.

There's a thread on how someone replaced them. It makes a difference.

I imagine the idle on your car is compensating for a leak like this thus the idle goes super low at cold after the AAR closes up after a few minutes. When the motor heats up everything expands and you get your warm idle.

Wouldn't hurt to make sure the popoff valve is secure. Check the runner boots too if you can get to the screws.

I wish I could speak from experience that it will solve it but it's the last thing I have to replace an my CIS. I curse myself for not doing it 40K ago when I did my engine rebuild.

Hope some of this helps.

Like I said according to my US/Can PET it should have it, so try tweaking it if it's there. It's just a suggestion - I expect you will get some more.

I had the exact same symptoms on my C3 - was the vac limiter.

Oh yea. It's easy to see if the vac on the dist works. Suck on the port with the dist cap off and see the swash plate move.

You can also test it by plugging the vac line to see if that makes an idle difference.

Depends on the model. My '82 SC RoW (Australian delivery) has one. It was definitely involved in my high idle issues.

Also, check the (what used to be called a) breaker plate to make sure it moves smoothly. If it is stuck, your vacuum advance and/or retard will not move smoothly, if at all, and that can complicate your problem.

Matt

You've got a big leak. It has to be something simple like a hose off. The idle adjustment screwed in all the way should kill the engine.

I had a problem similar to yours a few weeks back...changed out WUR, AAR and AAV....to no avail. Finally found out it was a bad relay on the circuit that controls the heater element on the WUR and AAR....they essentially remained at their cold setting and made a real nice vacuum leak when warmed up.

It is a black one, easy to check, it is on the rear panel in my car ('75)

Dennis

Scott,

My car used to run very similar to the symptoms you describe - especially closing the idle screw and still having a fast idle. Checking the advance weights is a very good idea, but what oneblueyedog said was what finally fixed mine. It was caused by air leaking in around the phenolic tubes that hold the injectors. I was amazed at how bad these looked. You can pull the injectors and change their seals, then pull the phenolic tube that holds the injectors. Mine were old, crusty, and the seals were worse. The car ran like new after I fixed these.

Tighten and replace the cheap stuff first.

Good luck.

ROW would have it yes, not American, 80's had no air pump, a lambda control brain, and a freq valve. Also had the unique double pancake setup for the first time, a very different animal that year. The OP never indicated ROW, so unless he has a ROW, he doesn't have the afore mentioned part.

The diagram above is not for a US 1980 SC.

I see some mention of checking the injector and injector sleeve seals. I have already switched out the injector o-rings, but have not replaced the seals on the sleeves. I would have though that by spraying carb cleaner onto the injectors, and seeing no change, that I could rule out these seals.

Additionally, I have looked, but do not have a vac limiter.

Hmmm.

Pipe 46 in the diagram rubs against the fan housing. It may have rubbed a hole through. Fixed mine with JB weld.
Rubber hose 43 gets aged and cracked
Tighten up all of the clamps to the hose ends to where they are immovable 12, 15, 19, 20,44, 45, 48,
I have a clamp on 47a and b

Replace all of the Vac hoses with German hose.

Make sure hose 13 goes below throttle plate and 13b goes above.

Get a mirror and look behind the throttle plate to see if there are open vac ports. Cap them.

Do you have a pop off valve? Do you have a cracked air box from a backfire?

Check the vac line to brake system for leaks.

Check boot 18 fro cracks.

Check the tightness of clamps on the intake runner boots. (PIA and you may have to do a partial engine drop.)

Just throwing out ideas. I've felt your pain.

I used starter spray to vac leak check. RPM's went up.

Got a pic of your engine bay?

Pipe 46 is steel on the 80" US, has a rubber end that attaches below the cold start valve, then it branches in a "Y" to the decel valve and AAV, the picture above really has nothing to do with the 80 SC'

This is the 80" sans part 8A which was used in 82 and 83

http://www.pelicanparts.com/911/911_...8-83/1-7-3.JPG

Has this recently started, or has it been this way since you had the car? Did a shop do some work on the car prior to this?

You should check your AAR, since your start/warmup idle is a little low, also your WUR/cold & warm control pressures.

Most importantly, I also think you probably have the later type of decel valve, and an AAV. They are on the passenger's side of the engine. Older cars had the earlier one on the left as someone showed. Check the later version of the SC CIS diagram on this site. These things are oriented horizontally and look like thick disks. Check to see if all hoses are connected. These Decel Valves (aka vacuum devices) can be fixed by gently squeezing them in a vice. Search this for more info.

Paul, I actually just bought the car in May of this year, and immediately rebuilt the engine. Looking back on it now, I probably should have replaced the CIS hoses and intake boots at the same time.

I did check my AAR, and it appears to close fully when the car is warmed up. However, I'm probably going to try and clean the disk to make sure that there is nothing gunking up the seal. You are also correct about the Decel valve and AAV, and both hoses on both are connected.

You have vacuum lines attached to both the decel and the aav? You should only have the AAV hooked up. I know it's deceiving in that they both have nipples on the 80" but only one gets hooked up. In fact if the decel valve is getting vacuum you will get a very high idle. Later in 81 they went to a pancake without a nipple.

These vacuum devices can cause the type of problems you are having, but as others have said, there are other causes for leaks. Check the airbox, pop valve, injector seals, etc.

Most often though that decel valve is the cause of a high idle. As Scott says, you can try disconnecting one of the small hoses from the end of the valve and see what happens. It may bypass the problem. You may get a quicker return to idle speed, which some people like, and/or you may get a slight burbling from the exhaust or intake when the throttle is snapped shut.

Apparently squeezing the valve in the vice about 1mm was the factory fix for this.

You might try capping the valve nipple and/or just plugging the line w/ a bb and reattaching it.

Check Jim Williams' K-Jetronic site on rennlist. It's extremely thorough.

When disconnecting the hose to the decel valve, do I need to just block off the vaccum hose, or also the nipple on the valve?

smessing, did you ever got the fix to this?
thanks

I just solved the idle problem on my 1979 911SC from some hints from the forum.
I found that my linkage that went to the throttle body wasn't letting it closed completely. I legthened the accelerator rod a few turns out and that seems to have solved my 1 year idle problem. I was tinkering with the mixture and the idel screw getting it right only to have it increase when the car had been run for 1/2 hour.

#1, thank you. I had a high idle issue when warm up. Idle would increase to around 1800rpm. After replacing distro vacuum hose idle is now perfect around 900rpm.

Thank you

One more note,
 

This is a great thread an it finally helped me adjust my mixture properly. Just a note that is not mentioned, the mixture screw that is down inside the air box between the fuel distributor and air valve IS A FLAT HEAD on my 1980. I figured this out after poking for 1/2 hour with a bunch of allen wrenches.