High Idle (CIS) and a Perhaps Shocking Pic

[prattrc]

Hello All,

I'm having CIS issues. Isn't everyone?

A quick background...I've owned the car for a couple of months (76S), and I changed the distributor cap, rotor, and points a few weeks ago. Otherwise, it's as is.

The car has never really idled properly. It's always above 1100rpm, but sometimes rests around 1600rpm. The tach doesn't bounce around or anything, I've fiddled with the idle screw, but when I get it down to 950rpm, it stalls after a few miles. I haven't dared with the mixture yet; I'm working my way there.

In the meantime, I've been reading everything I could get my eyes on--Souk's many posts, CIS Primer, random Pelican threads (dozens and dozens), etc.

Today, picking up on a thread from this board and considering the possibility of a vac leak, I put a piece of cardboard over the intake and there was no change in rpm. Hmm. Do I have this right? Good news: found the problem. Bad news: have to find the leak.

Next, I pulled off the air box cover to inspect for cracks and to get a better look at the air sensor boot for the same. While I was in there, I did Souk's field test, first lifting the sensor arm, and the engine went rough instantly.

Way rich AND vac leak?

While in the box, I also saw something odd. See picture below:



What the funk is that orange thing? It's thin, flexible, and sealed with tar-like gunk. Bad blown-box repair? Source of the leak? Portent of a major pain-in-the-arse repair in my very near future?

Thoughts? Answer? Consoling comments?

Thanks in advance!

[tonypeoni]

What ever it is its common in sc's i had one with tin foil too.

[prattrc]

So, it's not that unusual?

[tonypeoni]

Im not sure but my sc ran fine with that tin foil thing. But i remember looking at it and thinking man this must be some hack job!

[tonypeoni]

if you have a vacuum leak and your car is running rich assuming it has a cat you should have a sulfur smell ?

[Jeff Alton]

I am thinking that was someone's attempt to fix a cracked airbox. Then they put the flap in so they wouldn't have to fix it again when it backfired.....

Cheers

[ianc]

I have never seen such a thing in my life! I'm assuming it's an ass repair job on a cracked airbox that you'll want to spend some time looking at. If you had a vacuum leak in the past, someone may have richened it up to compensate. I'd tear into that little wart and see what's under it.

I'm having CIS issues. Isn't everyone?

No! If properly maintained and in good working order, the CIS is the most trouble-free injection system you'll ever own!

ianc

[Mysterytrain]

Looks like someone drilled the flapper hole in the wrong place! Without getting into the ying/yang of CIS I'm thinking that you have an air leak in your system.

[Scott R]

Get rid of that airbox, that's not normal. Drop the motor, seal the CIS system, new runner boots, vacuum lines, intake gaskets and anything else that looks suspect. Our host has the best prices I could find on this stuff.

[LakeCleElum]

A 30 year old CIS systems needs many parts replaced. Intake boots, lines, etc....You can patch it up, but to do it right, follow Scotts advise......I did it in my '73.5 a few years ago. It's ran perfect ever since....

[Jim Williams]

Originally posted by prattrc
Hello All,

I'm having CIS issues. Isn't everyone?

A quick background...I've owned the car for a couple of months (76S), and I changed the distributor cap, rotor, and points a few weeks ago. Otherwise, it's as is.

The car has never really idled properly. It's always above 1100rpm, but sometimes rests around 1600rpm. The tach doesn't bounce around or anything, I've fiddled with the idle screw, but when I get it down to 950rpm, it stalls after a few miles. I haven't dared with the mixture yet; I'm working my way there.

In the meantime, I've been reading everything I could get my eyes on--Souk's many posts, CIS Primer, random Pelican threads (dozens and dozens), etc.

Today, picking up on a thread from this board and considering the possibility of a vac leak, I put a piece of cardboard over the intake and there was no change in rpm. Hmm. Do I have this right? Good news: found the problem. Bad news: have to find the leak.

Next, I pulled off the air box cover to inspect for cracks and to get a better look at the air sensor boot for the same. While I was in there, I did Souk's field test, first lifting the sensor arm, and the engine went rough instantly.

Way rich AND vac leak?

While in the box, I also saw something odd. See picture below:



What the funk is that orange thing? It's thin, flexible, and sealed with tar-like gunk. Bad blown-box repair? Source of the leak? Portent of a major pain-in-the-arse repair in my very near future?

Thoughts? Answer? Consoling comments?

Thanks in advance!

That whatever it is covers a drain for oil or water, or whatever might accumulate on the floor of the air box, to drain out. There was a hose that attached under the hole to allow the "whatever" to drain out on the ground under the car.

Who knows why folks cover the hole........ it has nothing to do with the air box, the part that makes up the manifold, and in no way comtributes to air leaks that spell trouble for the CIS. It is not part of the intake manifold proper. See photos below. The hole in question is in the center of both photos.

Put the palm of your hand over the snorkle on the air box's filter cover and see what you feel. This should result in a vacuum being pulled on your palm, and the engine slowing somewhat. If not, there may not be a good seal at the filter cover. Check this out first before proceeding further.

The air flow sensor does not have to move much to make the engine go rough. Depending on how much you had to move it, the mixture could be a little too rich or a lot too rich.

Air Box Top



Air Box Bottom



Hope this helps.........

[prattrc]

Thanks, all.

I did put my hand over the snorkel, and nothing happened. No dive in rpm, no rough.

So, if there's a leak around the cover--and I wouldn't be surprised, since it didn't seem to go on with authority--how do I improve the seal?

And, should I leave the orange membrane thing in the air box?

The engine went rough with very little pressure on the sensor arm.

This should reveal me as the ignorant newbie I am, but how am I supposed to get the handy mixture adjustment wrench ordered from our hosts into the mixture access hole? It seems to be about an inch and a half too long to fit into the space between the hole and the sound deadening material above the engine. I feel stupid. What's the trick?

THANKS!!!!!!!!

[Rick V]

JMO but if you suspect an air leak get a can of gumcutter or some kind of flamable spray cleaner (automotive), start the car with the airbox cover on and spray the suspected area.(the entire intake system) Use short small blasts so as not to hit alot of area. When you find the leak you should notice an increase in idle or a smothing out of the engine. When you find the area, allow the engine to go back to normal and re-spray the suspect area again to confirm you have found it. If you spray into the air intake you will see the results of introducing the cleaner into the system as when you find the leak.
By the way, Howdy neighbor

[Jim Williams]

Ray,

If you use the method Rich suggests, you should adust the mixture to be a little on the lean side so you can tell when the engine gets a richening from the spray. Otherwise if the engine is seeing a rich mixture already, it won't be able to react with an increase in idle speed. You can also use a propane bottle for this, with a flexible hose to get the propane in areas you choose.

You may have to cut down the length of the 3 mm allen wrench in order to get it to fit into the hole. Just trim off a minimum amount to start with so you don't overdo it. A tool too short is just a useless as one you can't get in the hole. A bench grinder is the best way to do this.

[wswilburn]

I understand that the airbox drain doesn't let unmetered air into the system, and so isn't a vacuum leak. But doesn't it let unfiltered air (i.e. dirt) into the engine? That's why I plugged mine.

[Jim Williams]

Originally posted by wswilburn
I understand that the airbox drain doesn't let unmetered air into the system, and so isn't a vacuum leak. But doesn't it let unfiltered air (i.e. dirt) into the engine? That's why I plugged mine.

Scott,

You're quite right about the unmetered air, and also that this hole, albeit small, could possibly let some dirt into the system. However, the way these came from the factory, at least early in the stages of CIS progression in the 911, was with a rubber hose that attached at the airbox and ran down to a metal fitting that attached to the front of the engine which had a rubber valve, for lack of a better term, at the bottom. This valve was provided with a slit at the bottom that supposedly would open under the weight of the water or oil, but had a small enough open area that dust or dirt entry was held to a minimum.

One problem with this setup is that the valve, being made of rubber, would harden over time, and would also pick up oil and dirt, and plug up. I think many people would eventually disconnect this arrangement over the years, and the rubber tubing and the metal fitting would eventually disappear as later owners would remove the items, not knowing what they were there for in the first place.

The hole in question is pretty small in relation to the area of the air filter, and the location of the hole is not nearly so exposed as the filter. So I think that leaving it open probably doesn't create a problem. But I don't think that closing it up is necessarily a bad idea, either. IMHO, of course.

[jdowty3]

You should also check to see if the Auxilary Air Regulator may be stuck open and allowing extra air in.

[emcdan]

Boy....you sure can can alot of opinions. Some simple...some not. Well here's mine. That unpredictable idle sounds like a vacuum leak but could be a mixture problem or both. You can't rule other things either.

I would spend an afternoon removing and inspecting the airbox, then a pressure test. Move on to the intake and any potential leaking hoses. Once confident that any leaks are eliminated, adjust your idle to spec and then mixture.

I took a rubber handled allen wrench and cut off 3 inchs. It works perfectly for the mixture set screw. There are plenty of instructions here for getting your air/idle mixture close.

Good luck,
Eric