CIS Idle Speed and Mixture Setting Without an Analyzer

[911 tweaks]

usually 1-3 complete 360 degree turns...DEPENDENT on how many, if any vacuum leaks are present...= no leaks it will be fewer turns from my experience...
***side on a bit rich vs a bit lean...= best for engine longevity & performance...

[Jay Laifman]

Thanks!

[MPDano]

Well CIS is hard to adjust without proper gauges. Right in the center of those is just to get it close. Now, with CIS, everything has to be working as it should and "no" vac" leaks. WUR get's adjusted with pressure gauges and with specific temps.

If you are sure all your CIS components are working correctly, I would also invest in a Wideband O2 Sensor setup. I have that in the "Common Fixes" Thread to help you.

[papamamapup]

Need help please! I took my car to remove stuck transmission filler plug but when I went to pick it up my car no longer run. The mechanic offer to remove the CIS unit to check but he won't tell me how much so, I refuse the offer. My car ran very good and always start right up in second. Before I tow my car back he told me he will make it run and he said seem like The gas mixturn is to lean but after many hours he still did not get it run so, he offer to fix it for me but I refuse because my car was running perfect before. I've tow my car home by AAA and did some investigation. I found out that the air and gas mixturn was turn all the way off which mean you can't turn anymore lean. Now, i am try to turn it back on but don't know how many turn should I turn to get the car start? I have been working on it for 3 weeks everyday and got my car smell clean but now it' dead. I notices that when I try to start the car the RPM guage swing up all the way so, I think he much mess up something. When I was ther he mention that he can make the car can not start and nobody can find it that's make me worry. I bought this car running condition and only thing it need was a oxygen sensor and relay. After I tune a little air and gas the car ran perfect but now don't know what to do and I am very tired.

[tirwin]

Let's separate out a few things:

With the car off turn the adjustment screws the opposite direction and count how many full turns it takes to go full stop the opposite direction. Then turn it back to approximately halfway. Hopefully that will get you to a reasonable starting point to where you will be able to get it running.

Setting the mixture to get it running does not mean everything is ok. To get the mixture right you really need to take it to a shop that has an exhaust gas analyzer. That also assumes everything else is ok - fuel pressures, no vac leaks, etc.

You need to find a local shop you can count on. Post a question asking for recommendations in your part of town.

The tach needle comment... Well, you took the car to the wrong guy. Sounds like he created a problem so you would have to leave the car with him to "fix" it. No telling what he dorked up. It's going to be hard to go through every possibility over the Internet. Someone who knows these cars inside and out could probably spot it pretty quickly in person. The path of least resistance here may be taking it to a reputable shop.

That being said, I'd look for obvious stuff. Is the transmission ground strap disconnected? Are all of the CIS sensors connected? Is the 12-pin harness wire at the back of the engine connected? Plug wires tight? CDI box connected? Check the connection to the CSV. Operating under the theory that the guy was a lazy douchebag, my first guesses would be that he just disconnected something that would be hard to spot but easily accessed.

[papamamapup]

I was very happy that after I replaced the oxygen sensor and the relay the car run very good. The only think I did was turn down the fuel mixture less than half turn. I drove it around my home for many day and it was very smooth and always start right up. Anyway, I will check the stuff that you have mention today and hopefully I can get it run. The guy even won't give me the receipt for remove transmission filler plug. Now, It like start from the zero again!!!

Thank you,
Kent

[Vegas928]

Well, when I did it on Mein Fraulein (she had been neglected for a very long time, and some jackleg cobbled a bunch of "fixes") the answer was "not much" either way. But it was definitely necessary because the WUR hose was just laying on the manifold. Number 2 spark plug wire was, too... and ALL the plugs were less than hand tight. The spacers weren't even compressed.

I did discover it is easier to do with the airbox completely off so you can see what you're doing.

[Jay Laifman]

This is just a bump for CIS folks. Ironically, as I read through it, I came to the point that I had posted in here before myself. I guess it just shows how long I've enjoyed this car and still keep it running.

But now I'm going to ask for more clarification. Here is what MotoSouk wrote ages ago:

"If you move the air plate up slightly with a resulting rough or surge, you are closer to the rich extreme. If you have a 3mm Allen wrench handy, you can turn the mixture screw counter-clockwise to lean it out a little, maybe 1/8 of a turn, then repeat. To get it just right, you’ll have to develop a touch and maybe even a sense of smell. To test for lean, you can pull down on the arm slightly and get the opposite effect of the rich test. That’s it! That’s all there is to it."

If you pull down slightly and you are lean, you get the opposite effect of the rich test. What is that? A drop in rpm instead of a surge?
If you push up, and you are lean, does nothing happen?
If you pull down and you are rich, does nothing happen?

Here is my initial thoughts (which I reserve the right to delete when I later find how wrong I am!)
When lifting, the primary effect is to cause more gas to enter. So that means if you are already rich, you're making it even more rich. But if you are lean, you are adding needed fuel. Why doesn't that cause a surge?
And I you pull down, reducing gas, and you're rich it should be smooth, right? But if you are lean and you pull down reducing gas, it should stumble, right? So that's not the opposite of the rich test - it's the same result.

[Schulisco]

Originally Posted by Jay Laifman

If you pull down slightly and you are lean, you get the opposite effect of the rich test. What is that? A drop in rpm instead of a surge?

The height of the sensor plate gives a ground setup for the mixture over the whole rpm curve. That's why you should check first and foremost the right height setup of the sensor plate before manipulating everything else on the CIS...
The CO relevant fine tuning will be done by the CO screw - always afterwards! In early CIS models there was a bendable spring which provides the resting position for the sensor plate.
Later (as well on SCs) - there is a screw to perform a far more precise adjustment for the resting position of the sensor plate.

Originally Posted by Jay Laifman

If you push up, and you are lean, does nothing happen?
If you pull down and you are rich, does nothing happen?

No, it shouldn't.
When you're lean and you pull up manually the sensor plate a bit, then the mixture richens, possibly to a proper mixture only measurable surely by CO tester.

When you're rich and you push the sensor plate down, the mixture gets leaner. When the mixture is too rich, it may be more optimal then. But as well same applies here - precisely measurable and adjustable only by CO tester. That interval between correct and incorrect setting is so narrow that it's definitely impossible to adjust it without a CO tester...

Originally Posted by Jay Laifman

Here is my initial thoughts (which I reserve the right to delete when I later find how wrong I am!)
When lifting, the primary effect is to cause more gas to enter. So that means if you are already rich, you're making it even more rich. But if you are lean, you are adding needed fuel.

Correct.

Originally Posted by Jay Laifman

Why doesn't that cause a surge?

It depends on the mixture itself. It will cause a surge of the mixture if it is rich enough.

Originally Posted by Jay Laifman

And I you pull down, reducing gas, and you're rich it should be smooth, right?

Correct.

Originally Posted by Jay Laifman

But if you are lean and you pull down reducing gas, it should stumble, right? So that's not the opposite of the rich test - it's the same result.

Correct.

Don't forget the idle screw. It also has an influence on the flowing speed of the intake gases. That means plaiyng around on the mixture with the sensor plate height and the CO screw are not the only adjustment points for mixture on idle which is being used as metric for the emissions.

You have to think in intervals and sliding windows: Every adjustment point (height of sensor plate, CO screw and idle screw) operates in a working/sliding window. That means - if you richen the mixture on the sensor plate height, this influences idle speed and CO setting/emissions. And vice versa if you turn the CO screw this affects also idle speed and mixture and they must probably checked and adjusted again afterwards. This is continous game until the mixture is optimal not only on idle but as well in all operting conditions. And so you can see that as well the condition of the rest of components of the CIS system, like injectors, WUR and AAV, have a significant influence.

Thomas

[Jay Laifman]

Thanks!

[Jay Laifman]

FWIW, I just went and did this. I would use different words to describe it. Lightly lifting when rich caused a noticeable stumble. A light lift when lean caused RPM to increase - I wouldn't call it a surge. Pulling down was irrelevant since the difference between rich and lean when lifting was obvious.

The plus side is that it cured the problem I was trying to address. I recently fixed my WUR and was getting idle to be stable sometimes, but then sometimes idle would fall and wobble up and down. By leaning the mixture it took that away.

I had been adjusting the decel valve to see if that could fix it. It didn't.

Even after I leaned it out and got rid of the wobbling idle, I did have to set it toward the rich side to also make it nice and smooth.

Also for further guidance to anyone else, I had to rotate the mixture screw (not the idle bypass) about 3/4 of a rotation to go from the undulating idle to a lean mixture (where the RPM would increase when the throttle plate was lightly lifted). Then I backed off that - so probably 1/2 a turn got rid of the sometimes-undulating idle to a smooth idle.

[Jay Laifman]

I'm providing follow up info for anyone who might come this way in the future.

As I indicated, I lightly lifted my throttle plate and it stumbled - meaning it was rich. I rotated my mixture screw 3/4 of a turn and when I lifted the plate, the rpm went up - meaning I was then lean.

I drove the car. The fluctuating idle was gone. But the car ran a bit on the rough side. So I rotated it 1/8 a turn at a time and went for a drive. I ended up going about 1/4 more turn total and it smoothed out and the idle was still strong.

If I went a little richer still, I would get a light pulsing/flutter on very light constant throttle - very light, but with focus, it can be felt. The car is running great now - idle strong and no light flutter, and 1/8 a turn in either direction is not as nice.

I was thinking that I needed a CO meter or O2 meter to get this right. But with such a small difference left now, I can't imagine the meter would really help. I will still give it a 1/16 turn each way and live with it for a while, and see if either direction is even better.

Note, I was slightly suspicious that my Throttle Position Valve could be incorrectly positioned and allowing for the richness to occur at idle and also just off of idle, which could be causing the flutter on light throttle. So I used a clamp to stop the gas from flowing out of the TPV. There was no noticeable difference in the light flutter. I'll double check with the pressure gauge at some point.

[boyt911sc]

Originally Posted by Jay Laifman

I'm providing follow up info for anyone who might come this way in the future.

As I indicated, I lightly lifted my throttle plate and it stumbled - meaning it was rich. I rotated my mixture screw 3/4 of a turn and when I lifted the plate, the rpm went up - meaning I was then lean.

I drove the car. The fluctuating idle was gone. But the car ran a bit on the rough side. So I rotated it 1/8 a turn at a time and went for a drive. I ended up going about 1/4 more turn total and it smoothed out and the idle was still strong.

If I went a little richer still, I would get a light pulsing/flutter on very light constant throttle - very light, but with focus, it can be felt. The car is running great now - idle strong and no light flutter, and 1/8 a turn in either direction is not as nice.

I was thinking that I needed a CO meter or O2 meter to get this right. But with such a small difference left now, I can't imagine the meter would really help. I will still give it a 1/16 turn each way and live with it for a while, and see if either direction is even better.

Note, I was slightly suspicious that my Throttle Position Valve could be incorrectly positioned and allowing for the richness to occur at idle and also just off of idle, which could be causing the flutter on light throttle. So I used a clamp to stop the gas from flowing out of the TPV. There was no noticeable difference in the light flutter. I'll double check with the pressure gauge at some point.

Jay,

You could use the pull down/push up techniques and install a AFM for your troubleshooting and they work provided you have no unmetered air going into the system. So the prudent course of action is to test and confirm the absence of unmetered air.

I contacted MotoSook many years ago to correct and revise his post. It was too late to do an edit according to him. His contribution is good and helpful but missing clear instruction about unmetered air which is the Achilles of CIS.

Tony

[Jay Laifman]

Thanks. I am very happy with how it is running. But I've read your other posts on smoke testing. So I just found one for sale and ordered it. I also see a lot of folks, including you, with instructions to make one. The price I found it for is good enough to let someone else do it this time!

I'll report back any results if they are meaningful.

[Jay Laifman]

I am happy to report that I got a smoke tester and I had no leaks in the air box or intake hoses. The only light smoke I got was around a couple of the injectors. Any thoughts if this is meaningful?

But maybe the vacuum under operating conditions pulls the injectors into the seals and seals it off - where as with the smoke machine, the outward pressure does not allow the seal to work.

I will say that it took me about 5 different types of plugs to get smoke to not leak at the intake. Lots of trips to the hardware store and creative attempts.

The car continues to run great. Note that I did replace the air box about 15 years ago, and the runners more recently. I did replace the injector seals about the time of the runners. They are a pain to do, and they don't impress me as being all that great of a seal. I do recall at the time that the suggestion was to use some sort of special grease to put around them for the seal. I did use that.

[porschedude996]

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[angelny911]

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