'82 911SC Erratic Idle

I am hoping that someone can shed some light on my problem. I have an '82 911 SC with 120,000 miles. When the car is first started it idles smoothly. The problem occurs as the car begins to warm up. Once the car has been running for approximately 5 minutes it begins to idle very erratically and the car eventually goes dead. Does anyone have information as to what could be going wrong? Any information would be greatly appreciated.

Check things that are affected by temp changes, especially the starting injector and make sure it is not letting fuel in as the engine warms up. If there is a warmup regulator, make sure it is working okay, ie open when cold, closes when hot.

Also, have your shop checkout the idle mixture. It sounds like your problems begin when the warmup circuit cuts out, and a lean idle mixture would cause rough idle until the engine fully warms up.

[dudemagpod]

I have the same problem with my 1980 SC. When I start the car the idle goes on high 2500 rpm then it eventually lowers and then zigzags rapidly between 500 and 2500 RPM. Did you figure it out? Any help would be apreciated.

[ossiblue]

Originally Posted by dudemagpod

I have the same problem with my 1980 SC. When I start the car the idle goes on high 2500 rpm then it eventually lowers and then zigzags rapidly between 500 and 2500 RPM. Did you figure it out? Any help would be apreciated.

One of the main causes of symptoms like those you describe is too rich a mixture due to improper fuel pressure from the Warm Up Regulator (WUR ) or fuel mixture screw.
First try to establish that your fuel pressures are in specs, meaning the WUR is functioning correctly--this is the component most likely to be out of adjustment. The WUR lowers fuel pressure in the CIS system when cold, causing a richer mixture. As the engine warms and the WUR is heated, the pressures increase, leaning the fuel mixture. A wandering, hunting idle as you describe is a symptom of an overly rich mixture.

Testing the fuel pressures requires a gauge that is easily obtained, but any Porsche mechanic can test your pressures and that, IMO, should be your first step. Adjusting the idle mixture screw is a very delicate task, and should not be done unless the fuel pressures are in spec. If you use the search button on this page, you will find many threads on CIS pressure and WUR. If you are a new owner and not sure of the workings of your car, I'd suggest taking it to a known, experienced Porshce 911 mechanic to get things set up for smooth running. Then, at least, you'll have a baseline from which to measure changes in operation.

Oh yeah, welcome to the board and post some pictures of your car. I took a risk of getting banned for offering advice before a picture was posted of the owner's car !

[81turboporsche]

i had that problem with my 81 turned out to be a bad relay under the passenger seat ,changed it because it had gotten wet and the problem went away ,if you run the car pull the relay out and see if it evens out at a low rpm range a bit rough but safe

[Scooter]

10 years!

Now that has to be some kind of record to revive a thread that is nearly ten years old.

[81turboporsche]

whoa nelly i didnt even realize , i feel bad if they still have that problem

[euro911sc]

When is the 10 year b-day for Pelican? Looks like its soon as that post was all guests before registration was opened!!

-Michael

[NEWFIE 69 911E]

Originally Posted by Kevin Fairchild

I am hoping that someone can shed some light on my problem. I have an '82 911 SC with 120,000 miles. When the car is first started it idles smoothly. The problem occurs as the car begins to warm up. Once the car has been running for approximately 5 minutes it begins to idle very erratically and the car eventually goes dead. Does anyone have information as to what could be going wrong? Any information would be greatly appreciated.

My SC acted like this when I first acquired it. When I removed the engine to replace the numerous leaking oil seals, I noted that the metal air tube, that runs around the back/right side of the CIS unit, had developed a hole from rubbing against the oil breather hose.

I filled the hole with metal bonding resin, and viola - no more erratic idle! Worth checking...

[mike5876]

Originally Posted by 81turboporsche

i had that problem with my 81 turned out to be a bad relay under the passenger seat ,changed it because it had gotten wet and the problem went away ,if you run the car pull the relay out and see if it evens out at a low rpm range a bit rough but safe

where is the relay? what does it look like? my car is doing the same thing mike

[GothingNC]

Originally Posted by mike5876

where is the relay? what does it look like? my car is doing the same thing mike

It is under the passenger seat, usually a silver square part

81 SC Oxygen Sensor Relay

[SHShockley]

I've got this exact problem with my '82 911SC. It's got 135K on it. Once warm the idle will jump up to about 3K, then just as fast, go down to about 500. Frequently the car will stall. I can generally play with the throttle to get it to settle down, but not always. This problem first happened only when the air temp was cold, but has progressed to the point that it does it when it is cold or hot.

My initial thought is that the warm up regulator is bad. But looking at the price for a rebuilt one, I'm hoping it is something else!

Any thoughts before I take it to the shop?

Thanks

[slw911SC]

I just went through all this and the 3 magic words are: Auxiliary Air Regulator (Valve).

You can fix everything else - like clean out the tank, replace the fuel pump, fuel filter, warm up regulator, fuel distributor, fuel mixtures, fuel pressure adjustments, fuel lines, idle setting, injector O rings, injectors, injector patterns, vaccum seals etc. etc. (and you should check all that), but it's almost guaranteed that the AAR is the prime candidate.

They're mostly out of production (at the moment), but available at Parts Heaven - with your old core for a reasonable price. +1 for those guys!

[NEWFIE 69 911E]

Hi again,

I not already checked, it might be worth checking some of breather plumbing, as per my earlier message:

My SC acted like this when I first acquired it. When I removed the engine to replace the numerous leaking oil seals, I noted that the metal air tube, that runs around the back/right side of the CIS unit, had developed a hole from rubbing against the oil breather hose.

I filled the hole with metal bonding resin, and viola - no more erratic idle! Worth checking...

Here is an image of the tube, and damage:




Hope this helps.

[Jeff_Ragsdale]

I am having the exact same problem with my '82 911SC - idles great at startup, dies and is hard to start at intermediate temperatures (like the second stoplight from home ), and then idles better when hot.

I am having a continuing problem with blowing fuel relays, as well, that may or may not be related. I have chased that problem off and on (mostly off) for most of two years. Everybody needs a hobby....

Jeff