MOTRONIC: Adjusting Idle & Part Throttle Mixture?

[WydRyd]

I'd like to lean out my idle and part throttle mixture a little as my car is consuming a lot more fuel since the new AFM was installed (has new plugs, cap and rotor already).

Can anyone provide some guidance on how much I should turn out the mixture screw on the AFM?

I'm told to screw it in (using a 3mm allen key) until the idle drops and then screw it out approx 1 turn to lean it out.

Without a gas analyser, I know this isn't the most scientific way to tune the AFM, but is it close?

Advice appreciated

[ZOA NOM]

When I had my AFM refurbished, it came back with the mixture screw adjusted way rich to "protect them from liability" from a too lean mixture causing damage to my engine. That's what they said, anyway. I had the CO mixture adjusted, and it worked fine.

I have found that even a 1/2 turn on the mixture screw has an immediate affect, so I would recommend you take it to a shop with a gas analyzer.

[greglepore]

Its close, but do it with the ISV disabled.

[ianc]

There is a procedure wherein you measure the voltage off the O2 sensor as the car idles until you reach just around that 1 volt (I think) that indicates the correct mixture. I don't recall the specifics of doing this, but it should point you in the right direction. Search is your friend!

ianc

[WydRyd]

Thanks guys.

Ian, I haven't run an O2 sensor for years, so that's out of the question.

Greg, to disable the ICV/ISV I just jumper that test port on the left side of the engine bay, correct?

Maybe I'll just wait until the car goes in next week for a valve adjustment and have the shop do it properly with a CO gas analyser

[ianc]

Maybe I'll just wait until the car goes in next week for a valve adjustment and have the shop do it properly with a CO gas analyser

With all this massive Motronic troubleshooting you've been doing lately, you're still not doing your own valve adjusts? For shame.

Having the shop do it would probably be the best I think,

ianc

[450knotOffice]

I'll second that.

[WydRyd]

hehe, IanC, I would love to tackle the valve adjustments myself, but I don't have the tools, nor do I have a garage, so I'm leaving it to the PRO's (this time round). I've read up on how to do it and it sounds relatively easy, however, my turbocharger sits right beside the lower left valve cover, so the turbo would need to be removed to do this job properly. Not as easy as on a stock NA 3.2 engine

[ianc]

my turbocharger sits right beside the lower left valve cover, so the turbo would need to be removed to do this job properly

Hmmm... That does sound like a bit of a beeyotch, so I guess you're forgiven.

ianc

[WydRyd]

LOL!

Correct me if I'm wrong, but the A/F mixture screw under the AFM only affects the idle and light throttle A/F ratios, correct?

[ianc]

Correct me if I'm wrong, but the A/F mixture screw under the AFM only affects the idle and light throttle A/F ratios, correct?

No, I believe it affects the mixture across the board. Just think about it: it is allowing unmetered air past the flapper, so that happens no matter what the throttle setting,

ianc

[greglepore]

Yes, just use a jumper. This should get you in the ballpark; the problem you might run into is that the air bypass and the mixture screw interact to some extent. Its easier to set the base mixture w/ a gas analyzer or by reading the voltage off of the O2 sensor. Since you don't have an O2, that's not an option. What you look for on the O2, in case you care, is a rapid flutter btw 0 and 1 (millivolt, iirc). That means that the base mixture is in a range that the O2 can dither it.

If you do this yourself, keep in mind that its a small allenhead (3mm I think) and that the afm comes from the factory with a plug over the screw that you need to drill out-so it has to come off again.

(Edit-the dithering described above only happens when you monitor the voltage with the sensor connected to the DME, what you're actually seeing is the voltage change due to the DME adjusting the mixture)