Idling speed versus outside temperature

[Fernando.Vidal]

Dear Friends,
My Porsche is a 1981 911 SC, six cylinder 3.0, recently bought in Texas, U.S., and shipped to Vienna, Austria, where I live. Great car!
The only problem is when I start the engine early in the morning and the outside temperature is very cold. The idling speed goes up very high, to around 2000 rpm, and stays there for a long time, until the engine warms up. This doesn't happen when the car sleeps overnight in the garage, where the outside temperature is 70 degrees fahrenheit.
This problem makes driving and shifting gears very difficult.
Since this car lived in Texas, where the weather is warm, and now lives in freezing Austria, I thought that maybe I should replace the oxygen sensor or the cold start valve. But I only want to spend money on a new part if I'm absolutely sure that it will solve the problem.
I used to have an Alfa Romeo 155 which had the same problem. I disconnected the battery off and on again and the problem was solved. You know, these new cars with their computers ... You just have to reset them ...
I did the same now with the 911 but it didn't help.
Any hint?
Best Regards,
Fernando

[47silver]

hi:

I think that is the way your engine is supposed to run in the cold...You should not replace anything without reading some threads here on the CIS system....You also should get a set of gauges to evaluate the pressures in your system.

the cold start valve only works when the starter is engaged, so that should not be a concern.

Your sc has an auxillary air valve that may keep it idling higher when cold,,, mine 75 does not have it so check the posts here on aav and warmup regulator etc.

[Fernando.Vidal]

thank you. I will do that. Reading this forum is the best way to learn from other's experiences.

[jason2guy]

what u can do is modify the AAV, the one with an electrical plug. you basically limit the amount of travel of the block off plate inside the unit.

[Paulporsche]

The AAR is what establishes how long your revs stay high during warmup, not the AAV. Pelican Mystery Train has a thread on repairing the AAR.

Your condition of starting @ about 2000 and gradually going down to idle speed, which should be about 950, sounds good. It should take about 5 min in cold weather to do this.

[Fernando.Vidal]

Thank you. I guess I will have to take a look at both the AAV and specially the AAR. Problem is the rpm stays at 2000 much more than 5 minutes. I don't know how long, because at about 7 or 8 minutes waiting I turn off the engine or just start driving.

[Fernando.Vidal]

oh, I forgot to mention, if there is a way of simpling disconnecting these AAV and AAR devices. What I really like is to have full control of idling when cold. I want to be the one who decides how many rpm's and for how long when the car is cold, just like in cars with carburetors and manual throttle. Can I do that by disconnecting the AAV and AAR? Can they be disconnected??

[T77911S]

check for 12v at the AAR. that heats it up so it does not idle high very long.
second, the AAV could be closing too slow. that closes based on engine vacuum. check for air leaks in the plumbing to it.
my money is on the 12v though. also check 12v on the WUR.

[47silver]

75's have a manual lever adjacent to the heater controls that allow you to increase decrease the idle
you will find though that you will have to keep the idle up with the lever perhaps as long as you do know with the later year devices installed.

[Fernando.Vidal]

thank you all. complex issue this CIS. But I guess that once you start working on it and taking the parts apart, all the complexity disapears.

[snbush67]

Sounds like its working exactly as intended. You do not have to let the car warm up to drive, simply drive "Easy" until the car reaches normal operating temperature then you can drive "Normal".

On the 78 the thermo valve kicks off at 68 deg. F but that is measuring ambient temperature in the engine compartment. This of course is different than your 81 but the same theory applies, if it is 0 deg. F outside is is going to take a bit for it to reach 68 deg. in the engine compartment and you want the engine running rich and at higher idle to avoid the costly expense of replacing your air-box.

I don't think you have a CIS problem, just bad weather.

[Rikao4]

last week it was a bit cold in south Texas..
mine did this..not 2K ..around 1500 for me..
back out and go..
upside next summer..
when your sweating at 30 Cel..
your Texas car is laughing..
hot around here starts at 35+

Rika

[Pazuzu]

Yes, a Texas car doesn't mean it's lived a warm life

Mine has been hitting close to 1500, maybe 1700 on these early mornings, just above freezing overnight. Start it and drive it immediately (takes a bit of clutch work for the first 2 or 3 blocks). You can feel the two thermo switches when they click over, the idle and drivability changes significantly.

I'm usually up to normal idle within 4 or 5 minutes of slow driving, even when it went below freezing at night. I get good heat even before then.

[T77911S]

the warm up time for the WUR, and AAR is not very long, 3-4 minutes. most complain theirs drops the idle too soon, IE, the engine is not warmed up enough and the idle is down to normal and may cut off it is cold outside. the TTV is even shorter, 20-30seconds. these 3 devises are heated by 12v. if the 12v is not there, then the time it takes these things to warm up is a LOT longer, because the engine itself has to warm them up. if i understand your problem, it is taking a very long time before the AAR gets warm and thus lowers the idle to normal. check the 12v to the AAR and check the resistance of the heating element, i think it is the 30 ohm range. that is not critcal, if it is very high, as in an open, that is bad.

[Gunter]

Fernando,

Sounds like the CIS is working fine given the temps you've mentioned.

It is NOT recommended to warm up the engine without driving it. Start, wait a minute and then drive, keeping the revs below 4000.
What oil are you using? Hopefully not 20W50.
Are you actually driving in the Winter?
If not, don't start it until Spring; just leave it alone.
In the Spring, for the temps in Austria I'd recommend 15W40 Diesel, same temps here in BC.

Before doing anything, get the Bentley SC Repair Manual and read about the components for cold-start.
Leave the CIS alone for now and wait for Spring.
If you have problems shifting, check the components like the coupler and make sure the clutch is adjusted correctly.

[snbush67]

Originally Posted by Fernando.Vidal

oh, I forgot to mention, if there is a way of simpling disconnecting these AAV and AAR devices. What I really like is to have full control of idling when cold. I want to be the one who decides how many rpm's and for how long when the car is cold, just like in cars with carburetors and manual throttle. Can I do that by disconnecting the AAV and AAR? Can they be disconnected??

Fernando,

I hope you have logged back on and read the post, your CIS is working as intended if you chose to disconnect your AAV and AAR and whatever else, you will risk a backfire through your intake which could (even with a pop off valve installed) crack your air-box.

You are in the rare population of people who have a CIS that is working as intended, please take care of it.

If you want carbs then get carbs it is an easy replacement for your car, you can bolt on some Weber 40's and be up in running, install hand throttle and you have total control without the risk of backfire damage.

Shane

[Fernando.Vidal]

Originally Posted by Gunter

Fernando,

Sounds like the CIS is working fine given the temps you've mentioned.

It is NOT recommended to warm up the engine without driving it. Start, wait a minute and then drive, keeping the revs below 4000.
What oil are you using? Hopefully not 20W50.
Are you actually driving in the Winter?
If not, don't start it until Spring; just leave it alone.
In the Spring, for the temps in Austria I'd recommend 15W40 Diesel, same temps here in BC.

Before doing anything, get the Bentley SC Repair Manual and read about the components for cold-start.
Leave the CIS alone for now and wait for Spring.
If you have problems shifting, check the components like the coupler and make sure the clutch is adjusted correctly.

Gunter, from what I've been reading here, I think you're right about my CIS being OK. I was afraid of driving with cold engine with RPM at 2000, but you say it can go up to 4000, so I guess I was wrong. Regarding oil, I haven't changed it yet since I bought the car and I know it is using Synthetic Mobil 20W50. I just bought new oil, as I intend to change it soon. I bought mineral Castrol Magnatec 10W40. I decided to use mineral because of the very low mileage I do each year, so I thought it would be a waist of money to use very expensive Synthetic, made to last more than 10 thousand miles, and simply throw it away one year later with less than 4 thousand miles. I suppose that regarding weather, there is no difference between mineral or synthetic; the difference is in the thickness, so if I use a mineral 10W40, I will be ok for cold temperatures, as long as I change it once a year. Please correct me if I'm wrong. Now I don't understand why you recommend oil for diesel engines. I have the Bentley Manual (the car came full of manuals). I have it next to my bed to read a little every night. As to driving the car in winter, you are right once more. Last weekend I tried to go skiing, and the experience was a total disaster. I didn't get there because, without winter tires, the car skided badly. I came back home frustrated and with the car full of road salt. The shifting is fine, even in high RPM's, only a little bit hard from first to second, but I read that this is normal. Thank you so much for your help. Best Regards, Fernando.

[Fernando.Vidal]

Originally Posted by snbush67

Sounds like its working exactly as intended. You do not have to let the car warm up to drive, simply drive "Easy" until the car reaches normal operating temperature then you can drive "Normal".

On the 78 the thermo valve kicks off at 68 deg. F but that is measuring ambient temperature in the engine compartment. This of course is different than your 81 but the same theory applies, if it is 0 deg. F outside is is going to take a bit for it to reach 68 deg. in the engine compartment and you want the engine running rich and at higher idle to avoid the costly expense of replacing your air-box.

I don't think you have a CIS problem, just bad weather.

you are right, very bad weather. the temperature was -9 celsius when the idling went up to 2000.

[Fernando.Vidal]

Originally Posted by snbush67

Fernando,

I hope you have logged back on and read the post, your CIS is working as intended if you chose to disconnect your AAV and AAR and whatever else, you will risk a backfire through your intake which could (even with a pop off valve installed) crack your air-box.

You are in the rare population of people who have a CIS that is working as intended, please take care of it.

If you want carbs then get carbs it is an easy replacement for your car, you can bolt on some Weber 40's and be up in running, install hand throttle and you have total control without the risk of backfire damage.

Shane

thank you. although a prefer carbs, replacing now a CIS by carbs would require a lot of thinking (and money). So I would only do it if my CIS was completely damaged and I see now reading these posts that my CIS is ok. Maybe it needs only minor adjustments and cleaning the AAV and AAR, but I will leave this for the future. But thanks to you I know now that replacing CIS by carbs is possible.

[Gunter]

Fernando beim Heurigen oder im Grinzing.

You'll find that the majority of 911-owners use Dino oil, NOT synthetic because experience has shown that air-cooled engines leak more with synthetic.

I like Diesel oil because it has additives for pressure and heat.
15W40 for cooler climates is just right, IMHO.
Dino oil is a lot cheaper than Synthetic and can be changed more often.
Why would you be using 20W50 in below Zero weather? It's almost a crime and your engine doesn't like it plus it adds to more time to come up to operating temperature. Start, wait a minute, then drive keeping it around 3k with careful shifting until the temp needle moves.
Driving in the snow? Hmm.......Why?
The heat exchangers, flapper boxes, muffler...........the whole rear end will acummulate all that sand and gravel mixed with salt.
And the worst is to park in a heated garage to really let the salt go to work.
First chance you get when it is warmer go under there and use a pressure wash to clean it all out. (On a cold engine, of course)

Get yourself a cheap beater like an old Volvo 240 and store the 911 in the Winter with a full tank and extra pressure in the tires.

BTW: The AAV can not be cleaned or serviced. The AAR and WUR can be cleaned IF THEY ACT UP. If it works, don't fix it, as the saying goes.
The WUR and AAR get 12V only with engine running (Or with jumpering the fuel pump) The electrical plugs have a small wire clip, tricky to remove with a very small screwdriver. If the CIS works, leave it alone but learn more about it through reading.

Servus.

Originally Posted by Fernando.Vidal

Gunter, from what I've been reading here, I think you're right about my CIS being OK. I was afraid of driving with cold engine with RPM at 2000, but you say it can go up to 4000, so I guess I was wrong. Regarding oil, I haven't changed it yet since I bought the car and I know it is using Synthetic Mobil 20W50. I just bought new oil, as I intend to change it soon. I bought mineral Castrol Magnatec 10W40. I decided to use mineral because of the very low mileage I do each year, so I thought it would be a waist of money to use very expensive Synthetic, made to last more than 10 thousand miles, and simply throw it away one year later with less than 4 thousand miles. I suppose that regarding weather, there is no difference between mineral or synthetic; the difference is in the thickness, so if I use a mineral 10W40, I will be ok for cold temperatures, as long as I change it once a year. Please correct me if I'm wrong. Now I don't understand why you recommend oil for diesel engines. I have the Bentley Manual (the car came full of manuals). I have it next to my bed to read a little every night. As to driving the car in winter, you are right once more. Last weekend I tried to go skiing, and the experience was a total disaster. I didn't get there because, without winter tires, the car skided badly. I came back home frustrated and with the car full of road salt. The shifting is fine, even in high RPM's, only a little bit hard from first to second, but I read that this is normal. Thank you so much for your help. Best Regards, Fernando.