Hi everyone. I am still looking for a vacuum leak on my 87 16v. It is large enough that I had to bump the mixture to make it idle. It is also causing the climate controls to only give me heat (not enough vacuum at the mono valve?) As the motor warms up, the dash vacuum guage appears to increase vacuum. Is that a result of the aux. air valve closing off?

I have listened with a stethoscope, sprayed carb. cleaner and pulled vacuum with a hand help pump on all the rubber lines and hoses.(including the hose and fitting on the bottom of the air flow neter) No luck.

Is the vacuum module on auto trans. suppose to hold strong vacuum? Mine appears a little limp. Does it control the firmness of the shifting?

I am thinking of blocking the vacuum fittings one by one to try to isolate the problem. Any other ideas? It must be a fairly big leak, but it sure is elusive. Thank you.

Tinker,

Your last sentence indicated that you have reached the same conclusion I did while reading your post. Block off as many accessories as you can. Don't overlook the egr valve which is basically a calculated vacuum leak. Also don't overlook intake manifold, etc.

Good luck,


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Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles