how badly can motor mounts effect engine (87 300e)

[dirtysocks]

today, I started up the 300e and it was shaking pretty bad. The Idle sounded irregular, it seemed to fluctuate between how it usually idles and a lower idle, at which point the car would shake. There was no real change in rpm on the gauge as it fluctuated, So I was thinking maybe it was not purely an idle problem, and maybe just the mounts. The engine was shaking quite a bit more than it usually does. The belt tensioner (black shock looking piece to the right of the dist. cap), which used to make an annoying rattling noise only when the car was in reverse, is now making the noise all the time.

Two questions:

1. Should I start to look for a problem outside of the mounts (I plan on replacing them regardless), or can the motor mounts alone be the culprit?

2. Should I replace the belt tensioner as well, or with the new mounts keep this piece from rattling?

[gmercoleza]

Click to read My Motor Mount Thread. Note: My motor mount is now for sale on eBay, I think it has a couple days left. Let me know if you're interested.

[pberku]

Collapsed motor mounts can affect idle speed in that they can allow the engine to tilt while accelerating, decelerating, or idling. This can result in a pulled or released accelerator cable, that in-turn can lead to unexpected acceleration, and high, or unsteady idle RPM. Resulting in what you describe as poor idle.

Start by replacing both your motor mounts (If deemed necessary, than see if you still need to deal with the belt tensioner, and engine shock.

Also check your accelerator, cable and make sure its not too tight or too loose.


Phil

[MTI]

If your radiator has a plastic neck for the hose attachments, additional engine vibration from bad motor mounts (and other sources) can lead to premature cracking of the neck.

[anthonyb]

If the mounts get really bad, they can also affect the alignment of the driveshaft enough to throw it out of whack, which will give very severe vibrations at all speeds.

Did the shaking start suddenly? You could have an ignition problem, which will make the engine run out of balance (basically). I've seen a few spark plug wires go out and do this.

In order to solve the belt tensioner noise you will have to either shim the upper mounting point for the belt tensioner damper, or replace the damper.

[daddiojiggy]

i was wondering if motor mount life is time or mileage dependent?