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Re: Air Flow Meters

Hi Scott

I marked my response with *

regards
Werner


______________________________ Reply Separator _________________________________
Subject: Air Flow Meters
Author:  Non-HP-sd (sd@domain.elided) at HP-ColSprings,mimegw2
Date:    7/30/96 4:20 AM


Werner,
Thanks for your posting re air flow meter behaviour and workings. I 
have some questions relating to the idle adjustment screw.

1/ Does its setting affect anything if the system is within the Oxygen sensor's
   range to fine tune the mixture ?
   
   * I assume you mean the mixture adjustment on the air meter.  It generally
   * will not affect the rmp.
   * Yes, it affects the cold running mixture at idle, and if set too far from
   * the design center, it may cause the closed loop system to run 'at the
   * stops'.  That is there may not be enough adjustment range in the computer. 
   * but that's unlikely.
   * At any rate it effects the low rpm, low power part of the engine range

2/ What is the correct procedure to adjust the idle screw, as the computer and
   oxygen sensor will vastly change mixtures from the idle screw position.
   
   * This depends on the car or computer system.  On the L-jetronic you set the 
   * mixture adjustment to a voltage on the computer using a voltmeter (it puts
   * the setting at mid range) for some of the cars.
   * On some cars you remove the Oxygen sensor, and then set the CO to .4-.8%.
   * If there is no Oxygen sensor, you adjust it to 1.5 - 3% (early EFI BMW's)
   * I am not familiar with the Motronic system on your BMW, nor do I speak from
   * experience on a BMW.
   
   

In respect of question 2 I suspect to ensure the idle screw position is 
correct you would need to reset the computer's "learnt" ideal mixture setting 
buy momentarily disconnecting the computer, then disconnect the oxygen sensor, 
start the engine and adjust the idle mi screw "open loop" then reconnect the 
oxygen sensor.

* I don't know. There are some people knowledgeable about the Motronic on the 
DIY mail list.  Try posting your question there.

I am right or on the wrong track ?

regards,
Scott

1989 535i
1975 2002