CIS problems

Hi everyone,
I have a little problem which I'm sure it has to do with my CIS system. I apologize for the long story but here it is. Every morning I start my car up, the idle shoots up to 1800rpm...I'm sure that's normal, high idle from auxilary air regulator, right? After about a minute, the idle goes down to between 500-900rpm...there's the idle hunting right here, at about 120 degrees F. On the days where I actually drive until it reaches operating temperature(176F), the idle is normal, at about 900rpm and there's no idle hunting. Any suggestions? Thanks!

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Jeff
1976 911S

I'm not sure if that is a normal thing (your idle shooting to 1800 rpm upon startup). I too have a CIS and mine does not go past 1000 rpm when I start it.

Could your CO mixture be affecting this maybe??? Anybody??

Tim

Classic warm up regulator problem. I have the exact same thing happen to my car, especially when it's cold out. (either it stalls or gradually corrects itself within a few seconds.)
There are ways of checking the unit, maybe someone else can give you some more specifics.

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Leland Pate

___79 SC Targa

Hunting at idle is generally an indication of a lean mixture.
Bob w.

I don't believe I have the specifications but there should be an electrical resistance spec across the element in the WUR. The real test is with a pressure gauge, measuring fuel pressure. CIS systems frequently lope a little at idle, when they're running great. Rhythmic fluctuations of more than a couple hundred rpms is normal wiht CIS, but I associate it with the lambda sensor. 1800 at startup sounds high. Mine just goes to 1200, and there are no palm trees where I live (higher idles are normal for COLD engines).

You may be describing fairly normal behavior, but I'm not sure I know what idle hunting is.

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'83 SC

This is a '76 2.7L with CIS correct? And the problem only occurs at start up when cold, goes away when warm? If these things are so then you can eliminate everything but the cold start controls such as Leland mentioned. My '78SC will idle at 1000 to 1200 at startup in the winter and settle to around 800 or so after a few minutes. The CIS systems on the two cars should be very similar with no Lambda (this came in '80). A CIS schematic for the '76 will locate and identify the different cold start control devices on your engine for you. I immagine Pelican has this.

Hi,
thanks to everyone who have replied. I have thought that it was exactly this; a warm up regulator problem. My last unit showed no resistance, so I ordered a rebuilt unit and installed it. It seems to be running better, but I still have this problem. It doesn't get very cold in Hawaii, I would say maybe 65-70 degrees F in the morning. I will try adjusting the CO soon...how do I know what to adjust it to? Yes, RarlyL8, this is a '76 2.7 CIS, with no Lambda. How does the CIS schematic look like? I have the factory manuals; are they in there? My cold start valve is new, so I'm assuming that it isn't part of the problem. Yeah...I guess 1800 rpm at startup is kinda bad...and it wakes everyone up in the neighborhood! The only reason why I thought this was normal is because I went to see another '76 911 and it did the same, so I thought it was normal...I guess not. Thanks again for all the replies.

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Jeff
1976 911S

Living in Hawaii, your cold start valve should never come into play.
You need to check your co settings (mixture) and your fuel pressure before replacing any more parts. Check them when cold, during warm-up and at operating temp.
Bob w.

Rufblackbird (Jeff),

You live in Hawaii??? So do I....Oahu (Ewa Beach). If you're interested there is a local Porsche mechanic that I would highly recommend. He cured the same exact problem I had with my 73 2.4L CIS. If you want drop me a line at the following: enost001@hawaii.rr.com

Tim

Bob is right, I think. Find out if your fuel pressures are in spec. If not, replace (probably) the WUR. If so, and you want the idle to behave itself on startup, you could put a restriction in the hoses that attach to the auxilliary air regulator. At operating temperatures, this thing should be blocking air passage anyway.

But again, I associate a loping idle with the lambda sensor. if your idle is erratic, you may have fluctuating fuel pressures, or perhaps air is cavitating as it moves past your air flow sensor. Just ideas, as usual, hoping one will turn useful.

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'83 SC

Here is a cheap trick to solve your problem! Install a 10 ohm / 10 watt resistor in the power wire that goes to the warm up reg. The reg. connecter has two wires going to the power side of the reg. One is power to the reg. heating element and the other goes to the aux. air reg.

By installing the resistor in-line your warm-up cycle will take longer and allow your engine to get heat into it. The short warm-up cycles were done so that the cars would meet smog.

Good Luck,
Lee

Thanks everyone.
Bob, I will check my CO and fuel pressure. Superman, thanks for your ideas, I will look into them. Tim, were you at the meeting last night? If so, are you the one with the red targa? Oh, and yeah, please tell me who you recommend. Thanks!

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Jeff
1976 911S

As you know your '76 cis is fairly straight forward. With no lamda control(no feedback) your static mixture stays the same, unless acted on by outside forces. In normal warm running only the varing hight of the sensor plate caused by the varing air flow regulates fuel flow.
In cold start you should have only 2 things coming into play.
1. warm up regulator to richen the mixture.
2. auxilary air to speed up idle.
Without data (fuel pressure and mixture) I would guess too much air is getting in at cold start and causing too fast an idle speed. With data, my guess may change.
Bob W.

Jeff,

Yup, that was me in the red Targa! I DO remember meeting you....small world eh? You know Gerard from the meeting? He owns and operates Motorwerks down off of Ward Ave. The number is 596-7758. Good food huh! LOL!
See ya soon,

Tim

I took a closer look at my tachometer yesterday. Between the "0"(which is not there) and the "1" there is one tick mark. I'm assuming that's the 500 rpm mark. Between "1" and "2" there's 4 tick marks, I'm assuming it's 200rpm increments. My high idle is at the 4th tick mark above the "1", so I'm assuming it's idling at 1800rpm. You guys say yours idle at 1200rpm...if I just counted the tick marks and assumed that each was 200rpm increments, I would be at 1200rpm. Is my tach markings off?
Lee-I think a minute of warmup is long already, but I'll keep your idea in mind. Thanks.
Bob-I will go ahead and check the CO and fuel pressure. If my friend doesn't have the necessary gauges, I guess I'll have to take it to a "real" Porsche mechanic. Thanks!
Tim-Yeah, I know who you're talking about. Sean(Cripps) told me I should go talk to him. Yeah the food was great! This was the first meeting I went to and I'm sure I'll keep coming! Thanks!

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Jeff
1976 911S

[This message has been edited by Rufblackbird (edited 06-17-2000).]

Thanks to everyone to have replied. About 45 minutes ago I enriched the mixture by one tick(or notch). I started the car and it immediately sounded better. The idle still shot up to ~1800 rpm, but I believe it came down faster than usual. There was a bit of idle hunting, but I took it out for a drive and didn't notice it any more. Usually when I go for this type of drive in my valley the temperature does not reach even close to 180. Today I went, say about 4 miles and it was reaching 180 already. Is this normal? I sure hope it is because it runs much better warm. When I came home, the engine was warm, and it idled beautifully. It made my day. I did notice that I averaged 15.5mpg during the last fill-up. The gas tank is 21 gallons, right? Say...if I don't have that fuel overflow tank installed, will it affect my effeciency? Sorry for babbling on, and thanks!

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Jeff
1976 911S