Surging Idle

[brianhiggi]

I have a '78 SC that had been sitting outdoors for a few years. I got it started but when the engine warms up the idle starts to go up and down. I have read on other threads that the warm up regulator may be at fault. I took the wur apart and didn't see anything that looked amiss but I don't know exactly what to look for. Could the idle problem be something else?

[twistoffat]

Vacuum leak

[Bob Kontak]

I bet the WUR is ok. You probably are sucking false air.

If you have a vacuum leak the fast, cheap and dirty test is to get some starting fluid or carb cleaner and while the engine is idling spray the fluid on the connections where air can be sucked in (on the engine side of the air sensor). The idle will change when a leak is found.

This may not work as good as other tests for small leaks but a small leak won't cause problems.

Spring the four bucks and you can eliminate a big set of variables. Use the stuff at your own risk, too. I have never had a problem but I try to aim real carefully.

Put your WUR back on and get pressure gauges if you want to go that route.

[Targalid]

Another possibility is that your mixture is too rich. At cold start this is OK but when the engine warms the extra fuel will cause your idle to hunt. Try adjusting the mixture if the search for air leaks is not productive. If you haven't done this before Calling911 has a great post on adjusting the CIS without gauges. It takes a long 3mm Allen wrench to do this. Harbor Freight has a complete set including the size you need with neat plastic handles that make adjustment a breeze. I keep the 3 mm Allen wrench right next to my American Express Card and I don't leave home without it. Actually I keep it in my tool kit and sometimes will stop by the side of the road to make a small adjustment. Once you get it set it stays in tune for quite a long time. After being parked for so long you likely have deposits in your fuel delivery system. A couple of bottles of Techron may help your problem.

[boyt911sc]

Originally Posted by brianhiggi

I have a '78 SC that had been sitting outdoors for a few years. I got it started but when the engine warms up the idle starts to go up and down. I have read on other threads that the warm up regulator may be at fault. I took the wur apart and didn't see anything that looked amiss but I don't know exactly what to look for. Could the idle problem be something else?

Brian,

Start your engine and keep it running until you get into operating temperature (very warm engine). Driving it around is preferred than just letting it idle to get to operating temperature. Once the engine is fully warmed up, park the car safely and remove the oil filler cap. The engine RPM (idle speed) should drop down from 950 to 700 rpm more or less when you removed the oil cap. If you don't observe any noticeable idle change, you have unmetered air going into the system.

Lastly, think twice before you tinker the air mixture screw!!!! I would not recommend touching it until you have verified and confirmed that you don't have a vacuum/air leak. Not being able to find one does not mean you don't have a leak. So a pressure test is required to avoid the guess-work. Keep us posted.

Tony

[scotricker]

mine too,
My 78 SC has the surging idle, only when cold, right after start-up, and only for a few minutes. When warm, it idles just fine. When I remove the oil cap, the idle rpms go down some, but not too much because the engine keeps running as it should.
After reading Tony's comment, does this confirm that I don't have unmetered air leaks? I'm thinking again about leaning the idle mixture....

[Bob Kontak]

Tony is spot on with his advice. If it drops 250 rpm from 900 then you are ok. If it drops 50 rpm then you are sucking unmetered air.

Targalids advice is good on maybe too rich but it could easily have both problems.

[scotricker]

thanks, I will check rpm drop again this weekend.

[brianhiggi]

I took the oil cap off wen the engine was warm and the rpms did drop. It's hard to say how much because of the revving idle but it was noticeable. I got some carb cleaner and sprayed around a little but wasn't sure of all the place to spray. Is there a thread that shows pictures of the places to check? What are the most common places for a leak? Also I hear a hissing sound coming from the airbox, is is supposed to make a loud hissing sound?
Thanks again to everybody's help. I am a newbie.

[Bob Kontak]

Hissing is ok. Good work on performing Tony's test. Hang with us and you will get this. We were all noobs once - even Tony and Targalid.

Spray around the injectors where they connect into the intake runners. Also, the intake runners both ends. Around the rubber sleeves and where they bolt onto the heads. The head interface is where I had a two year PITA unmetered air leak. Made my car put-put-put slight muffled backfire when it idled.

Check the airbox over for cracks. Do you have a pop off valve installed on the inside of the airbox? That can leak.

What is the rpm range when it is surging? Does the exhaust stink like gas?

Do you have a tool to adjust the CO mixture? How many tools do you have available? Do you have an air compressor, dremel, vise, etc? Do you park your car on the street with no garage. Asking because there are limits to what you can do without tools or space.

How about the hoses that connect to the oil tank? You may be able to feel them for integrity rather than going nuts with the spray.

There is a hose that goes from your engine all the way to the brake booster in the front trunk. That can be a stinker sometimes and can crack near the transmission. Try finding that one if you are a newbie - LOL.

[Lorenfb]

"Another possibility is that your mixture is too rich."

Which is the most logical for a surging condition!!!!!

Have to love those, though, who always think it's got to be an air leak,
i.e. Must have done a 'Most Mentioned Post' search and concluded; "Let's post
that". Although, haven't seen that posted for when; "My cars pulls to the
left during a right hand turn." is the thread.

[Bob Kontak]

Originally Posted by Lorenfb

Have to love those, though, who always think it's got to be an air leak,

Take the time to read the posts in the thread. Pompous **** (Edit - I meant Pompous parakeet)

[Joe Bob]

Whooosh, one warning shot across the bow.....

[Bob Kontak]

Here are Simons CIS primer causes for irregular idle during warmup in order (with my commentary)

Leaks in air intake system (false air) (Causes lean condition)

Auxiliary air valve does not open (Causes rich condition)

Cold start valve leaking (causes rich condition)

"Cold" control pressure outside tolerance (Could cause rich - depends on what side of the pressure range it is outside of)

Injector leaking, opening pressure too low (Causes rich condition)

Injected fuel quantities unequal (rich or lean but per cylinder - don't think this would cause surging)

Basic idle setting incorrect (rich or lean - assuming this means both air bypass screw and CO setting - with your symptoms we default to rich)

Lambda control system not functioning properly (Probably rich)

Here is calling911's post regarding CO setting w/o gauges. It is pretty cool. There is a link to Soukus' thread as well in this one.

How to setup CIS with no gauges

The CO adjustment port is to the right of the air sensor housing. Between the housing and the fuel distributor. If you get the allen wrench set - (Harbor Freight Tools (801) 426-9935 155 N State St, Orem, UT 84057) - read these posts first. Seems relatively simple but I have a later SC that allows me to cheat by reading the O2 sensor signals.

On sale, baby!

http://www.harborfreight.com/10-piece-t-handle-metric-hex-key-set-37862.html

[Lorenfb]

More of the typical 'shotgun' approach to troubleshooting which typically occurs
that wastes time and money for the car owner, i.e. Info found on the internet
that's copied and posted that most likely is non-applicable but sounds good for
the poster to get his post count up!!!!!!!!!!!

[db_cooper]

A lot of sarcastic drama from L for another simple driveablity discussion....

[Bob Kontak]

Originally Posted by db_cooper

A lot of sarcastic drama from L for another simple driveablity discussion....

So this is not the first time he pooped in the punch bowl?

Have not seen the OP so Loren must be helping him offline.

[boyt911sc]

Originally Posted by Bob Kontak

So this is not the first time he pooped in the punch bowl?

Have not seen the OP so Loren must be helping him offline.

Bob,

This guy is a smart guy but does nothing to help other people except boosts his ego and make people look stupid. Search his posts and you'll know what kind of individual this fellow is. He was away from the technical forum for a while and now he's back..........disregard and ignore are my suggestions. Just my two-cents.

Tony

[Number1_dog]

I had the same problem with my 1979 911SC.

I found that the fix was a careful adjustment of the Idle air mixture (the small hole between the Throttle body and the fuel distributor that takes the 3 mm Allen) and the idle screw (a large screw with a spring that has a slot for a screw driver but can be adjusted by hand) on the left side of the throttle body.

If you turn the 3mm Allen clockwise you en-richen the idle mixture, and if you turn the idle adjustment screw counter clockwise you increase the idle speed. To check if the idle mixture was too rich I pulled a plug to see the electrode tip, black too rich, gray/white just right.

enrich the idle mixture a little, like no more than a 1/8 a turn of the 3mm allen, then see if you can use the idle adjustment screw to bring it down to 950 RPM. Blip the throttle in-between adjustments.

Good luck

[daniel911T]

Brian,

I'm not going to claim to be a CIS expert, but I have worked a lot on Bosch L jetronic systems (the follow on to CIS)

In general, DO NOT TOUCH THE MIXTURE SCREW! unless the rest of the motor is in perfect tune!

Before going there, check the condition of your plugs, confirm your timing, make sure the vacuum system to your distributor is working as it should, make sure there are absolutely no vacuum leaks, and check for proper functioning of the various engine sensors. *edit* Also, especially if the motor has been sitting, remove and clean your fuel injectors if you can, if you can't, then run some good fuel system cleaner through the tank (many swear by the Berryman B-12 products.) Everything must be clean, properly set, airtight, and running at the right pressure before you touch any of the screws on the throttle body. Generally, the throttle body screws are intended to be set by someone with an exhaust gas analyzer.

The #1 most common problem on a CIS car is vacuum leak. Especially if the car has been sitting. The rubber on and around the engine will eventually dry rot, or just dry and shrink. Check all the vacuum lines, replace if they seem even a tiny bit iffy. Especially check the large diameter ones, and where they connect to the main intake. As others have said, check the seals around the injectors themselves. Finally, check out the short rubber tubes that go between the main intake manifold and the runners that actually go out to the cylinders.

The vacuum leak is what you should be looking for first. It's the simplest and cheapest fix. You can test the fix with duct tape, then order the new part.

Best of luck!

-Dan