Setting Base Idle AFR

[aston@ultrasw.c]

My porsher has been running like a dog for months.

To cut a looong story short I adjusted the AFR at idle using a wide band O2 sensor and an LM-1. I jumpered out the idle control per Wayne's book P102.

Initial reading, 15.2 AFR. Obviously way lean.

I backed out the mixture screw in the AFM slowly. After about a full turn the AFR had dropped to 15. It was hard to keep track exactly (!). I kept backing it out and backing it out. I was afraid it was going to fall out!

Finally I hit 14.7 yay, and set the idle midway between 800 and 1000

I thought I had better stop there and go for a spin. The old dog ran great!.

So, should I keep on backing the screw out to get down to 14.5 or so, or leave it well alone?

Is measuring AFM accurate enough, or should I take it for a CO2 test?

Cheers!

[stlrj]

Originally Posted by aston@ultrasw.c

I backed out the mixture screw in the AFM slowly. After about a full turn the AFR had dropped to 15. It was hard to keep track exactly (!). I kept backing it out and backing it out. I was afraid it was going to fall out!

Finally I hit 14.7 yay, and set the idle midway between 800 and 1000

I thought I had better stop there and go for a spin. The old dog ran great!.

So, should I keep on backing the screw out to get down to 14.5 or so, or leave it well alone?

That's interesting, because backing out the CO adjustment screw on the AFM is how you make it leaner, not richer. Full in means full rich and full out is as lean as it goes.

[aston@ultrasw.c]

Originally Posted by stlrj

That's interesting, because backing out the CO adjustment screw on the AFM is how you make it leaner, not richer. Full in means full rich and full out is as lean as it goes.

That's strange

I was definately backing it out, unless it has a left handed thread

I will take it for a CO check/adjust to be sure.

[JFairman]

If your car has an operational oxygen sensor and lambda system it has to be disconnected before making adjustments to the air flow CO adjustment screw unless you know where it is at first and you what you're doing... or else it is trying to compensate for your adjustments at idle with the pulse valve on the fuel head.

[aston@ultrasw.c]

Originally Posted by JFairman

If your car has an operational oxygen sensor and lambda system it has to be disconnected before making adjustments to the air flow CO adjustment screw unless you know where it is at first and you what you're doing... or else it is trying to compensate for your adjustments at idle with the pulse valve on the fuel head.

I suspect I am doing something wrong. My test set up:

BC jumpered out (idle control)
O2 sensor removed
wide band sensor installed

thinking..........

BUT.....I did not actually disconnect the O2 sensor, I just left it hanging. Sounds like that could be an issue.

The DME could be fighting my "adjustment."

If I make enough mistakes I will be an expert eventually!