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Old 06-13-2003, 09:15 AM
sbourg sbourg is offline
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Join Date: Jul 2001
Location: SoCal
Posts: 1,303
I haven't put mine in, and will likely not for awhile. The big problem is, the ECU will use two sensor inputs to adjust the mixture via the EHA. From other posts and hints by Stevebfl, I believe the pot is the first line of information on change-of-demand by the engine, with fine-tuning at running speed by the lambda sensor. This will make adjustment difficult by a DIY without the Bosch recommended procedure in hand. I would count on having a final adjust done by a pro, if no one offers a suggestion up on this site.

As a first line of attack, however, it seems to me that IF you can get the pot set very close to the correct value at normal idle, you will likely not need any further adjustment. It is vital to put a reference scribe mark on the airflow meter body BEFORE removing the pot for any reason. Careful measurements with a caliper of any mechanical difference between the circuit board alignment on the new and old parts should allow a compensating rotation to take care of this issue.

Adjustment of the trimpot is a trickier issue. Although it can easily be just set to the same value as the old one, this might not be correct. The resistance element is a complicated multi-tapped design, and my experience with deposition techniques is that variance from sample to sample is highly likely. This is what the trimpot is designed to compensate.

My method will likely put a test voltage across the old and new pots, and measuring specifically at the geometric spot where the wear marks are worst (idle?), adjust for similar voltages at the element.

But best, maybe someone can post the actual in-situe procedure?

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