I would have your on/off ratio checked out if everything else in your igntion system has been checked or good. I was getting bad gas mileage until I adjusted my lamba. To adjust lamba you need a special tool.

For your second problem I would check the electronics out and the device out.

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)