1986 300E 160,000 miles. The Econcomy gage runs 1//2 when idleing. Step on the gas and the two middle vents on the dash stop blowing air, the side ones (by the doors) keep working. When coasting the economy gage goes to zero (left)and the middle vents really push out air. Cruise control is very jerky. Are these things related? What should I do to fix them?

Yes they are related. You have a vacuum leak somewhere. These can be tricky to find so you may want to seek help on getting a diagram for the vacuum sources.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Where is a good place to find a vacuum diagram for this car? Would the library have one or on the internet. MB sells a shop manual on cd for $100.00. Are you familiar with it and is it extensive in it's coverage? Thanks Larry

I has this exact problem on my '86 300E with 170K miles. My tech pulled the dash and replaced some vacuum pods (servo?. It worked great after that. Actually, my problem evolved to the point where there was NO air blowing out of the center vents. Coming from Houston this was totally unbearable!

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Mark Herzig
1992 500E (82,000 miles)
1987 300SDL (105,000)