My idle is still crappy and the turbo pressure is higher than it should be at idle (brakes are pretty weak). I suspect some vacuum hoses under the hood are toast and I am replacing them one by one with higher quality silicone. However, I suspect the brake booster and or the check valve maybe malfunctioning. I pulled the check valve and grommet and plugged up the brake booster hole and the vacuum end (couldn't get the hose off the manifold to check for leaks), but the idle is still crappy and the turbo pressure is still higher than it should at idle (turbo has been replaced). Is there a better (correct) way to test the brake booster? What else should I check?


This car (92 740) drives like the wind, very nice (best car I've driven except at idle), idles alot better since all the work i've done but not perfect. Now that is a lot warmer here it doesn't sound like a 81 Mercedes diesel.