Tweak Idle from 650 to 800 RPMs

dralph12 · 06-04-2008, 10:30 AM

My 86 911 runs great and has no issues except what the idle is low @ 650 once the car warms up. With the idle at 650 it is to low for the alternator to run correctly.
How can I just tweak the idle to 800? Is there a quick easy way?

Trog · Trog's Garage

I have a similar problem, low idle once engine has warmed up. The car runs fine, just low idle.

I know of no way to raise the idle as it's set in the Motronic. I wonder what's forcing it to idle so low? Must be a bad sensor reading?

ischmitz · ischmitz's Garage

Maybe mixture out of whack ? - do a search: there is a way to set the ICV to its center position and then adjust the air bypass screw in the AFM for proper idle base speed. Check Steve Wong's website 911chips.com for details.

Trog · Trog's Garage

Quote:

Originally Posted by ischmitz

Maybe mixture out of whack ? - do a search: there is a way to set the ICV to its center position and then adjust the air bypass screw in the AFM for proper idle base speed. Check Steve Wong's website 911chips.com for details.

That's what I thought, but I checked my CO and it's about 1.5%.

dralph12 · 06-04-2008, 01:32 PM

Thanks for all the info!!
I will check it out ASAP, and get back with a post

DRACO A5OG · DRACO A5OG's Garage

It sounds like it maybe running too rich.

I would check the base idle by jumping connections "B" & "C" in the driver side engine bay. it is the open relay socket. Once plugged in it should by pass the O2 sensor & ICV and you can verify if she is trully set at 800 RPMs.

If set at 800 RPMs: remove jumpered wire, Adjust the Air/Fuel mixture on the AFM. Clockwise to richen, Counter Clockwise to lean. then check RPM's again

If base idle is lower than 800 then simply raise the idle but you need to check air/fuel mixture so she wont run too rich. Caution, do not over lean her, it may damage the cylinder heads

I literally drove around doing this until I got to close to proper settings to eliminate sub-dips of my idle but using a CO reader would be the best tool for this for accuracy.

My ghetto 2 cents,

Jim

stlrj · 04:23 AM

Quote:

Originally Posted by Trog

That's what I thought, but I checked my CO and it's about 1.5%.

So your mixture is out of wack. Spec is 0.8% CO before the cat. If you're getting 1.5% after the cat, you're way rich.

Trog · Trog's Garage

Quote:

Originally Posted by stlrj

So your mixture is out of wack. Spec is 0.8% CO before the cat. If you're getting 1.5% after the cat, you're way rich.

My cat has been removed. I believe 1.5% before cat is reasonable?

tcar · 10:33 AM

Trog...

Spec is 0.8% CO BEFORE the cat.

Do you still have a lambda (O2) sensor hooked up?

ischmitz · ischmitz's Garage

The Porsche workshop manual say idle CO% should be between 0.6% and 1% and hydrocarbon < 300ppm. And that is before the catalytic converter with the O2-sensor disconnected.

stlrj · 06-05-2008, 08:06 AM

1.5% CO and no cat...how do you get it to smog?

Trog · Trog's Garage

I'm exempt from smog-testing as my car is deemed a "Collector". Plus out here in BC-kanada, I believe any vehicle built before 1988 does not need to have a cat.

Trog · Trog's Garage

Quote:

Originally Posted by tcar

No, Trog...

Spec is 0.8% CO BEFORE the cat.

Do you still have a lambda (O2) sensor hooked up?

Sorry, yes my O2 is still connected.

Trog · Trog's Garage

BTW, an 1984 passenger vehicle with a 3.2Ltr engine weighing 1300KG only has to meet these emission standards in BC:

Driving Mode HC Standard: 213 parts per million
Driving Mode CO Standard: 1.48 percent
Driving Mode NOx Standard: 2159 parts per million
Idle Mode HC Standard: 380 parts per million
Idle Mode CO Standard: 4.33 percent

My idle was 1.5%CO, well below our limits. My concern is fouling plugs.

stlrj · 06-05-2008, 08:32 AM

Quote:

Originally Posted by Trog

My idle was 1.5%CO, well below our limits. My concern is fouling plugs.

Setting it to spec might help prevent fouling.

dralph12 · 06-08-2008, 02:44 PM

Is there a way to read the Voltage, resistance, or current off the CO2 monitor that sits in front of the Cat. to know if you are between 0.6 and 1.0% without having a CO2 meter?
I have a Volt/Resistance/current meter and I'm license to use it!!!
I don't have a CO2 meter.

dralph12 · 06-09-2008, 09:08 AM

Im trying to understand when I will know I have the Air/Fuel adjustment right!!
what is a sub-dip. Is it when you let off the gas the idle drops below 400rpms for a sec. them jumps back to the normal idle?

ischmitz · ischmitz's Garage

Dan,

the response function of a narrow-band O2 sensor is very non-linear and doesn't really lend itself to do a mixture measurement with a voltmeter. The sensor produces a voltage close to zero when lean and close to 1 volt when rich. It is like a step-function Read and see here http://www.aa1car.com/library/o2sensor.htm

What you really need is a wide-band O2-sensor or a gas analyzer. These have a much more linear responses.

Cheers,
Ingo

dralph12 · 06-11-2008, 07:43 AM

I’m looking for the place I jumper out connections "B" & "C" in the driver side engine bay. It is the open relay?. I posted a pick of the open relay ! Can someone explain where "B" and "C" are so I can jumper them. There aren’t indicators on the panel

socket.

ischmitz · ischmitz's Garage

Yes correct. Read here on Steve Wong's website. It is explained well and there are the pin designations, too http://www.911chips.com/dmeconvr.htm