88 300SE Mixture adjustment problems
 

I am having problems getting my mixture adjusted. I followed the instructions in this link very carefully

http://www.landiss.com/mixture.htm

It is a california car, so I was able to push the X92 button (three times) to change modes and get the duty cycle to read 70% with the key-on not-running. Deflecting the air flow sensor yields 10%, and wide open throttle yields 20% as it is supposed to.

When running, I can adjust the mixture to yield 70% at idle, but @ 2500 rpm it moves steadily to 18%. If I lean it more so it is 35% @2500, then at idle it will move to 92% after 10-15 seconds. I tested the O2 sensor and with it disconnected the voltage is .7 - .8 @ 2500 and at idle the voltage drops to 0 or even -.03. Just off idle it is about .4 - .5. It seems to run consistantly lean at idle and rich @ 2500. The instructions say to try to get the readings within 10% (idle vs. @2500) and near 50%. When I disconnect the black/white stripe purge line I don't feel any suction. nor do I feel any on the other vacuum line connected to the sensor in the head near the valve cover. I see several other posts where people have adjusted the 2mm screw inside the EHA to help correct this, but it seems like the difference between idle and 2500 is much bigger in my case. Any ideas what type of malfunction would cause the air/fuel ratio to change so much between idle and 2500 rpm?

I also hooked up a meter to monitor the EHA current. There is a swing from 9ma at 2500 to -4ma at idle. This also seems to indicate that there is a mixture difference between idle and 2500.

I could use some suggestions here. After reading several posts I thought that I may have a vacuum leak that was causing the lean mixture at idle. I replaced the rubber between the throttle plate and the mixture control unit and both the idle valve hoses. I also cleaned the injector o-rings. I tried spraying brake cleaner in several areas when it was running and I didn't notice any changes in the engine speed, so I don't think I have a vacuum leak. I think this helped a little, but I still run a 35% duty cycle at 2500 rpm, and a 80% duty cycle at idle. This is no where near within 10%. Any ideas?