Idle too high??

keithbkeller · keithbkeller's Garage

Wow, I have a 1981 911 SC and have got it running really strong and finally figured out that I had two injectors that were not right and so everything is back to normal except the idle is high. I've got the big air screw turned all the way in to the stop and still I am idling at 2000 RPM? I have even taken off the rubber air dam that covers the throttle body and cleaned and tighten all connections and can't find a air leak anywhere? The car runs better than it ever has but won't idle down?
I even checked and cleaned the plunger and diaphragm and all hoses. Then had the mixture checked and set. What do you think could cause this high idle??

schumicat · 07-11-2013, 02:12 PM

test the aux air regulator

you can find instructions with a search, it is very easy

Bob Kontak · Bob Kontak's Garage

Classic air leak. The SC will stall or at least only chug (near death) at 200 RPM with the idle air bypass screw turned all the way in.

You got a big air leak. Check your air box flapper for sealing at the o-ring and base.

I use starting fluid/carb cleaner and while idling, spray it on the base of the intake runners, injector o-ring seals and all connections where I think an air leak can occur. This will find a big leak but not always a little leak.

There is a lot written up on this. If you want to do it right search on boyt911SC's posts with CIS Air Leak in the search criteria. His methods are fool proof at the expense of some time given you have to set the procedure up vs. just spraying a can of ether at potential trouble spots.

I found big leak with ether but only after setting it up like Tony suggests did I clear all the evil.

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by schumicat

test the aux air regulator

+1 This is a classic "air leak" - however, carb spray or pressure testing will not identify it.

Gotta do the leg work to knock out the variables.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by keithbkeller

Wow, I have a 1981 911 SC and have got it running really strong and finally figured out that I had two injectors that were not right and so everything is back to normal except the idle is high. I've got the big air screw turned all the way in to the stop and still I am idling at 2000 RPM? I have even taken off the rubber air dam that covers the throttle body and cleaned and tighten all connections and can't find a air leak anywhere? The car runs better than it ever has but won't idle down?
I even checked and cleaned the plunger and diaphragm and all hoses. Then had the mixture checked and set. What do you think could cause this high idle??

Keith,

You had the fuel mixture adjusted? Why? This is the most common mistake by CIS DIY'ers!!!!! And I bet my money that you had increased (rich) the mixture slightly to make it idle better. True or false? Keep us posted.

Tony

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by keithbkeller

...................I had two injectors that were not right.............. What do you think could cause this high idle??

Double check to see that your injectors did not pop back out of the holes. Given you fiddled with them, you may have stressed (tiny bend in) the metal lines enough for the injectors to be "sprung" up out of the holes.

As Tony asks, tell us about the mixture setting. Did it run fine after mixture adjustment and then the RPM's increased?

Joe Bob · Joe Bob's Garage

Find airleaks and put the exhaust on an analyzer. Bet it is runnig rich.

keithbkeller · keithbkeller's Garage

No, believe it or not I was chasing this damn fuel injector problem all around the car and started with draining the gas out thinking it was fouled, (which it was due to sediment in the injectors) then a new fuel pump, fuel filter, used enrichment relay, O2 sensor relay, O2 sensor, and are you ready for this? The throttle linkage bushings were shot and I was only getting about 50% throttle with the peddle to the floor! Oh boy this car has really woken up!! It is running like a raped Ape! SO after I got every thing running good I took it to my friend who is a Porsche mechanic and he hooked it up to his smog machine and dialed in the mixture control screw to get the mixture right. After that the idle is now way too high. I just don't want to turn him loose with the car for fear I will end up with a massive bill... So now I will start looking for a air leak! Thanks for your help!!

Joe Bob · Joe Bob's Garage

A Porsche mechanic after setting mixture and finding a high idle should give advise as to why there is a high idle.....so what was his input?

keithbkeller · keithbkeller's Garage

His imput was leave the car with me and let me figure it out! I said no thanks!

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by keithbkeller

His imput was leave the car with me and let me figure it out! I said no thanks!

I like that thinking.

Post questions, comments as you see fit.

theiceman · 07-12-2013, 01:07 PM

The guys in california would know better bug im not sure a " smog machine" is the right piece of equipment for checking base co
I would get an lm1 and do it again. That mixture is set wrong

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by keithbkeller

His imput was leave the car with me and let me figure it out! I said no thanks!

Keith,

He could be a really good mechanic but he may not be familiar with CIS (Ketronic). Find some one who knows the system well. You are a good example of someone trying very hard to fix the problem and probably working hard. It is not how hard you work buy how smart you diagnose the problem. All the problems we have discussed in this forum about CIS have been well documented. After all these years, I'm still searching for a CIS problem that a DIY'er like you or me could not diagnosed correctly. And I'm still looking.......name me one.

Give him (mechanic) the chance to prove his ability to diagnose the problem correctly. Even if he's doing right, it takes time to locate the culprit. The key to a successful CIS troubleshooting is to test and confirm. In case of doubt, test and confirm. Keep us posted.

Tony

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by theiceman

I would get an lm1 and do it again. That mixture is set wrong

Ok - we got an OP here that is trying. Toss out a little love and explain what an LM1 is.

He can go to Pep Boys and buy a dwell meter and do it on his own. Does he really for true/absolutely need an LM1 to get his 180 hp SC running decent?

What's an LM1? AF ratio sniffer?

Not dissin' you, bro, just trying to rationalize. I wish I had the coin to buy and analyzer. OP does not want to spend $250 or more on a wrench (which I think is awesome), so unless the LM1 is a buck eighty six we are going to pull teeth just to get him to spring $50 on a dwell meter.

I love you, Man!! Just throwing this out there.

tirwin · tirwin's Garage

I assume he means this:

http://item.mobileweb.ebay.com/viewitem?itemId=151076431925

I tend to agree with Bob though. Spend the money on the dwell meter. It is useful for troubleshooting the duty cycle of the frequency valve. If you really want to know AFR, get a wideband O2 with a narrowband output. But that is a "nice to have". The dwell meter and the fuel pressure gauges are more "must haves" in my book.