All good advise, I agree that what you are probably reading is the end of capability to correct a rich mixture. As was stated you are probably at the end of EHA correction at -10ma.

I just wanted to clear up this question you asked:

"My understanding is that if I depress the plate I should get about zero ohm, but the resistance does not change."

You were talking about the throttle switch and then made that statement/question. It sounds like you are talking about two different things. Depressing the plate sounds like you are refering to the airflow plate which is NOT the throttle and the potentiometer on the side of it is not the throttle switch. Just for clarification.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician