High idle problem- CIS

[davis911s]

I have a 77 with 2.7 CIS

I am havving an issue with a high idle that I can not bring down.

When I start the car (cold) my idle is about 3000. I can NOT bring this idle down.
- I unhooked the linkage so I know that the linkage is not causing it
- the idle stop screw (probably wrong name) is all the way in so it is not pushing the linkage up
- the idle adjustment screw is all the way clockwise, so I can not slow it down any more

The car starts great and idles smooth, just real high.

I have not taken it for a good run to bring it up to operating temps, I know this will probably bring the idle down a bit, but 3000 seems real high, even for a cold engine.

I did a quick check for vacuum leaks with carb cleaner but did not find any.

Another thing I noticed was that I can "turn" the distributor cap about 1/4" . I find it weird that there is free play with the distributor cap. I think the cap should be firm and not be able to change so freely. I changed cap and same thing with both caps. I did not "turn" the cap when the car was running. Scared to cause either a problem with the car, or SHOCK me )

Any ideas? Or is this normal idle speed for a cold engine and I should take it for a ride and get it to operating temps then check RPMs.

Thanks in advance

Shawn

[T77911S]

3 things to check. there is a big round disk in back on the right behind the fuel distributor. it is the aux. air valve (AAV). its purpose is to provide air, kinda like putting your foot on the gas pedal, when starting. as soon as the engine starts, vacuum pulls it closed and is no longer used. on the right side of the engine is the aux. air regulator. it opens when the engine is cold to idle it up. the AAR has an electrical connector providing 12v to the AAR to "heat" it up. once warm it is no longer used.
on the left rear behind the throttle body there is a device about the size of an egg. that is the decel valve. just as the name implies, it lets air bypass the throttle body when you let off the gas so the RPM's dont drop too quickly.
i dont know if the last 2 will make it idle to 3000 RPM.
move the throttle by hand just to makle sure it is closing all the way.

[davis911s]

Thanks
I moved the throttle by hand and it is closing all the way

As for the other three how do I check them to ensure they are working?

Shawn

[tcar]

Have you let it 'idle' for 3-4 minutes?

That's long enough for it to come down off high idle.

[wrx paul]

i had the same problem a few years ago, turned out to be this thing
http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_FULcis_pg11.htm#item37
I tested it by blocking off one of the pipes and it dropped my idle back to normal. Luckily I had one on my old 2.7 when I swapped to the 3.0 so I just used that one as they are a bit pricey for a new one.

[Paulporsche]

Check the decel valve. It is the small pear sized component just to the driver's side of the mixture control unit. Try taking the small hose off the top and see what happens. Try plugging the line and see.

The AAR is another possibility. Search it and poster "mystery train". He has a great writeup on adjusting it.

Do you have an airbox popoff valve? Is it functioning properly?

Try running the engine w/ the dizzy cap in one position, say all the way to one end of its travel.. Turn the engine off and reposition it to the other extreme. Restart and see what happens.

Have you checked your timing? Have you checked that the entire dizzy isn't rotating?

Make sure the vacuum line to the dizzy retard is on. Remove it see what happens.

Make sure your point gap is correct.

Make sure the shaft inside the dizzy turns smoothly and springs back. Maybe your timing is advancing and stuck.

Make sure the sensor plate isn't stuck.

[ossiblue]

As you can see, there are many reasons why a CIS might have a high idle--here's one more that I found caused the same problem on my car (after verifying all of the things mentioned in the other posts were not the problem.) There is a "multi-branch" vacuum hose that is located in the front of the engine, out of sight behind the intake/airbox hardware. It's difficult to see without a mirror, it's a molded piece with (I think) 4 braches. Mine was old and cracked at a joint that was impossible to see. It was only by pulling off the hose and looking at it closely that the split was discovered and the air leak found. If all the above do not remedy your fast idle, track down this hose. It's a PITA, but it solved my high idle problem.

[Paulporsche]

That hose LJ mentions is important. Many components, incl (I think) the decel valve and the vac retard, are "fed" by it.

[ossiblue]

I think this is the hose:

911-110-276-02-M100

It looks like the one I was talking about (from my memory) but I don't remember the clamp. Also, the part is for 78-84, and my engine is a 76. Maybe the clamp is a later version.