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From digest.v7.n937 Tue Jan 13 14:38:35 1998
From: (Eric Tangen)
Date: Tue, 13 Jan 1998 10:38:21 -0600
Subject: Re: Cannot pass emission at idle! Need help! (L-Jetronic)

>From: "Honjo, Shige-MSM" <>
>Date: Mon, 12 Jan 1998 06:22:00 -0800
>Subject: Cannot pass emission at idle! Need help! (L-Jetronic)
>I have a 83 E28 Euro 528i with L-Jetronic and I'm having trouble passing
>HC count at idle.
>The first time I tested the car, the HC count at idle was 1400 and at
>2500 rpm the HC count was 150. After the initial testing, I have
>replaced the spark plugs, spark plug wires, rotor, cap, fuel filter and
>air filter and adjusted the air flow meter and idle speed. The air flow
>meter adjustment was cranked all the way down to the "rich" setting and
>I have leaned it out and adjusted the idle speed promptly.
>I went back to re-test and the results did not change! I still have a
>idle HC count of 1400! What is going on??!?!? Anybody out in digest
>land have any experience with this? Please help!

this one isn't in *any* of the books that i've comes from personal it may be somewhat controversial.

i think your aux air valve isn't closing when the engine is warm.

to get a proper idle speed with this part not working properly, you have to 'midadjust' the throttle position stop and the idle speed adjust (the brass slug below the throttle body)

what this causes (i think) is an excessive vacuum at excessive, i mean wrt the design parameters of the air flow meter.

so your idle speed is correct, but the pointer on the potentiometer track on the air flow meter riding higher than it should, causing a rich mixture.

to check this theory out, do the following:

0. remove the black plastic cover from the afm. it is held

on by adhesive.

  1. with the engine at idle, move the pointer down on the track;

    there should be little change in the idle speed or character for at least some movement of the pointer on the track.

  2. to fix, get a new aux air valve or disable the function of

    existing part by plugging the ports on the intake. add some tension to the air flow meter mainspring by winding it using the toothed wheel. be careful-the wheel can spring out of control as you try to nudge the teeth around the keeper bar. its a good idea to paint a reference dot on the spring and the afm body.

  3. personal results: my 80 coupe, idle HC of 250-380 (previous

    owner records prior to my ownership)...i replaced the aux air valve, O2 sensor, dist cap, had injectors cleaned, did a valve job, and tightened the afm 9 teeth from its initial condition: idle HC is now 70, 2500 rpm HC is 7.

i also tightened the afm on my 78 530i after disabling the aux air idle HC down from slightly over 700 ppm to less than 100.

on a related note...if your l-jet car has got the distributor with the vacuum retard line that goes to that little dohickey on the t'stat housing...that system also impacts cold idle speed.

eric tangen
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