This morning I performed the test, copied below. It saw it on USENET (alt.mercedes)
Quote:
You need to determine if the load of being in gear causes the engine to
idle roughly or if there is another cause of the rough idle.
You can easily test this by idling the engine in D with the parking, not the foot brake, applied. How does it run in D vs. N?
The parking brake is entirely mechanical and uses no vacuum so the engine should run the same except for the load of being in or out of gear.
Now, with the transmission in D and the parking brake on, step on the foot brake. If the foot brake booster is defective you will see the difference in the engine idle as soon as you step on the foot brake.
A vacuum leak in the brake booster will dilute the air / fuel ratio and cause the engine to idle slower and roughly hence the lower oil pressure.
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My brake booster is OK, if this test is a good measure. When I shifted from D to N with the parking brake on, there was a rise in RPM when the car was cold. When I repeated that when the car was hot, there was no variance.
When shifting from D to N when using the foot brake, there has always been a brief rise in idle RPMs, before it settles back down. Am I correct in assuming that is normal?
So my task appears to be to look for loose, cracked or leaking vacuum lines.
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2008 E350 4matic / Black/Anthracite
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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black
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