I've searched the forum on vibrations at idle, didn't find any answers to my question, so I'm posting here.

It's a 1991 300d. Especially when the speed decreases down to the idle level in that last second before reaching absolute idle, then even at full idle, the car vibrates. Very annoying. Just started a few weeks ago. The whole car has that low vibration that hurts even your ears. If I rev the car slightly, the vibration goes away. Possible the idle needs to be raised?

I had 2 people look at the motor mounts, and they thought they were fine, plus they said if it were the motor mounts, you almost couldn't even drive the car; you'd feel it when even accelerating.

I just ran through 2 cans of Moly Lube, no difference on the vibration. It will happen even in park, so that takes the drive shaft out of the equation.

The only thing I can think of, is there's a bearing squealing slightly somewhere that I can hear when I have the car in park (probably does it when I'm driving too, but I don't notice it with the car windows up, and my mind on driving, etc.). Don't know if it's the a/c or something else.

I'm guessing maybe a clogged injector that is clogged enough to mess up the idle, or maybe the car has more miles on it than the odometer says (maybe someone unplugged it for a while) and the chain needs to be checked for stretching or something?

Any suggestions?

Thanks,

Jeff 1991 300d, 141k


Updating now that the problem was found..... even though the motor mounts appeared fine, they weren't. Someone told me to jack the engine up a bit (with a thick piece of wood under the oil pan so as not to puncture a hole in it) to take the weight off the motor mounts. I did that, and the vibration went away. We replaced the motor mounts, I went with the OEM Corteco brand, and the car is MUCH nicer now.

could be one of the motor mounts (there are four, not just two), or one of the shocks next to the motor mounts, or even the rubber peices which hold the bolts that hold the air cleaner in place. on my 300dt, i had a similar vibration as i slowed and stopped and the car was idling. replacing the motor mounts and air filter holders fixed the problem (and i, too, have a non-functional odometer)

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Do the RPMs dip below the normal idle point when you let off the accelerator? Mine does that (mainly when cold). I haven't been able to figure out why. It was a little better when I upped the idle, but the problem is still there. The only errant vibration is when I let off the pedal - no symptoms at high RPM.

What's the idle speed at?

Here's a video of mine about the RPM's dropping: http://www.youtube.com/watch?v=GbeXKXAWMXk

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1982 240D, sold 9/17/2008
1987 300D TurboW124.133 - 603.960, 722.317 - Smoke Silver Metallic / Medium Red (702/177), acquired 8/15/2009
262,715 and counting

Wow. Your idle drops down to 5. Mine is about 7. Also, sounds like your car could use some Moly Lube. Loud knocking.

I might check to see about getting the idle up, or like the other guy said, there's 4, not just 2, motor mounts. I'll check those.

Thanks.

My odometer works fine, just wonder if someone disconnected it for a 100,000 miles. Car runs great though, I have no reason to suspect that anyone disconnected it for a few years.

I will have to check the OTHER 2 motor mounts. I didn't know the had four. The other 2 are obviously hiding underneath, out of sight.

What are you're talking about, one of the shocks next to the motor mounts?

The dampner shock, as I think it's called, up front on the engine, the little shock absorber thing, has previously been replaced, it's fine.

Thanks.

What about your injectors, have you tested/rebuilt/replaced then?

I have not done any of those 3. The only thing I did today, was to run Moly Lube through them.

Someone earlier said there are FOUR engine mounts. I only saw 2. Where are the other 2? I have the bottom splash guard on, so I didn't get to see any others.

Someone gave me the tip of putting a jack under the engine, and lifting the engine slightly to see if the vibration goes away, which it did.

That means it's the motor mounts.

Mind you, the motor mounts have TWICE the thickness that someone else posted was the minimum. But it turns out, one gets pulled, the other gets squashed, depending on which way the drive shaft turns. Therefore, the one that gets pulled ... LOOKS fine, but it's not fine.