Your technique suggests a lack of awareness of how this system works.
The act of adjusting the mixture till something changes, is to overwhelm the system both ways with proper system activity somewhere in the middle. This system can not work right unless it works period. Doing the adjusting you have done guarantees that the system can't work.
Read the DIY article about Evaluating Engine Controls in the DIY section of this site. The testing is very simple and done with common tools.
When working properly the system can be properly adjusted and monitored with a decent voltmeter. If its broke, it gives diagnosable data.
Bosch Master, ASE Master, L1
33 years MB technician