What is the best method to set idle speed?
 

What is the best way to raise or lower the idle speed on a 3.2 Carrera engine? It is a Euro version car, if that makes any difference.

Thx.

I got this off of Steve Wong's website. If your car is pre (mid) 1987, then base idle is 800 RPM. If it's mid-87 or later, then the base idle speed is 880 RPM. Here it is. Just adjust your speed for pre or post '87. Good luck to you.

"To reduce the base idle speed if necessary to 880 rpm, adjust the idle speed screw on the throttle body by two to three turns clockwise. It may be covered with a yellow plastic cap, which will need to be removed. For a more exact adjustment, bridge B and C in the rubber test socket on the left side of the engine compartment (located behind the black removable cover) with a piece of wire, and adjust the idle speed to 880 rpm at normal running temperature. Properly adjusted, there should be no difference in idle speed with the jumper or without. Remove jumper when finished."

http://www.911chips.com/throttle.gif

http://www.911chips.com/BCbridge.gif

http://www.911chips.com/BC-socket2r.JPG

Maybe you need to replace your ICV (idle control valve).

What's the reason for jumping the B and C terminals in the test socket? Well actually you gave the reason but why does it give a better adjustment?

I think bridging B & C disables the idle control valve.

Now, how about on an 88 Turbo,
Thanks

I'm in the process of getting a scope on both side of the ICV but I think it works like this....
When you short pins B and C it forces the ICV to operate at the center of its PWM (pulse width modulation) then you adjust the "idle" screw to get the idle bleed the amount of air to support the wanted/centered PWM at the idle rpm wanted. When you take off the short the idle should not change.... and the idle speed very likely will not be different than when you started. The DME wants the idle to be a certain number and will adjust the PWM of the ICV until it gets there. One thing that can mess up the whole idle control function is if you idle switch is not activating. Check this with an ohm meter and feeler gauges to see how much slack you have. The spec. for my car is supposed to be just under 1 degree... this translates to about 0.5mm. Also check that you have the required play in the throttle "loop" under the car. If this is tight it will pull the throttle link and may pull the link off pressing on the idle switch.

I did a post on this in the last week.

True enough, but remember that the idle speed, as set by the bleed screw, will change according to engine temp. With the same setting of the bleed screw, the engine will want to idle more slowly when cold than when warmed up. The ICV should be constantly attempting to correct this, but even with all the recommendations for no change when removing the B-C bridge, I find my car still runs best if I set the bleed screw for no change when warm, then open it up another half turn. This seems too make it easier for the ICV to correct the idle when cold. YMMV...

ianc

I sort of assumed the idle bleed screw would be set with the engine warmed up.
Right now I'm thinking the purpose of the idle bleed screw is to adjust the bleed amount when combined with the ICV "centered" in its PWM range to result in desired idle rpm. When the engine is cold the ICV runs at a more open PWM but the resulting idle should be the same. This is outside of the mode when the engine is freshly started and the idle is high for a minute or so.
Probably the big thing I found so far on my engine was that the idle switch was way out of adjustment and the idle switch may not have been activated in many cases when it should have been.

I mentioned this on another thread I think... I took an ICV apart. It is very simple... like two dc electric motors... ground one side and it turns about 90 degrees one way.. ground the other outside pin and it turns from 90 to -90 degrees the other way. The total could be less than 180 I didn't measure that. If you take one apart and forget to mark the relationship between the base and top part you can look at the "pole" that has the two wires... center the mechanism and center the contact inside to the center of the pad on the "motor". This puts the contacts wiping back and forth on the center of the pads and not crossing pads.. which I think would be a short. The resistance across the pads are 22 ohm from center to outside pins and 44 ohms across the outside pins... or approximately this.

getting back to the original question... the way to raise or lower the idle speed is to have a different program/data put on the chip.... Steve W can do this if that's what you want.

Very old thread I know, but one of many I have referred to recently chasing an idle issue.


I have read both from below, so my question is:

With the car at operating temp do you shut the car down and bridge B and C with a jumper, start the car and then adjust the screw, shut down the car, remove the jumper and restart...OR...

...have the car running while bridging B and C, adjust, and then remove...again, with the engine running the whole time?

The latter is how I do it so I can hear the idle while removing the jumper after adjustment, but as I have read (somewhere here) both methods just wanted to verify.

I was thinking there was a technical reason for shutting down and adjusting that I wasn't aware of...

Thanks-
Erik

No reason to shut it off
With it running you can hear if the idle speed changes when it jumpered or not
Ideally there should be no change

Thanks-

That was how I interpreted things.


Erik