Fuel - Basic Idle Speed and Mixture Setting Warning
87BMW02GROUP 13 Fuel System
Bulletin Number 13 04 87 (1452) Page 1 of 2
Montvale, NJ August 1987 Technical Dept.
SUBJECT: Idle Speed and Idle Mixture
MODELS: All with Motronic M1.1
Information: NO ATTEMPTS SHOULD BE MADE TO CHANGE THE IDLE SPEED/IDLE MIXTURE BY MANIPULATING THE TAMPER-PROOF BYPASS SCREW IN THE AIRFLOW METER.
The basic idle speed and mixture setting, as adjusted at the factory, must not be changed, as it provides the exact parameters and threshholds for the proper functions of the adaptive idle speed, Lambda control and purge systems.
These three adaptive systems are interrelated and strongly depend on the basic factory setting. Any change of the preset bypass screw adjustment in the airflow meter will shift the pre-programmed regulation ranges out of their pre-set "centerline", thereby decreasing the adaptive capabilities (see TRI's 12 01 86 (2051), 11 04 86 (2054) and 11 05 86 (2056).
As a result, any influences that would affect idle speed and idle mixture (for example, purge vapors, diluted oil or air leaks) cannot be corrected to the designed parameter and might cause the "Check Engine" light to come on intermittently. In that case, even the installation of a new control unit or idle valve would not cure the problem of the "Check Engine" light coming on intermittently, making troubleshooting difficult for a technician who is not aware of the airflow meter tampering.
In case of "Check Engine" light complaints proceed as follows:
1. Connect Service Tester to engine and read out DME failure memory.
2. Repair according to the display of the Service Tester, also refer to S.I. 13 01 87 (1345) and 13 03 87 (1351).
Important: Please note that if the basic factory setting of the airflow meter has been altered, no warranty claims, including work relating to this alteration, will be accepted.