Engine vibration in gear/aircleaner vibration at idle? - PeachParts Mercedes-Benz Forum

rwthomas1 · #1 01-12-2003, 03:35 PM

Okay I have done some research and I would like an opinion on what to do next. At the NEgtg I noticed that some of the other 123's idled smoother than mine, specifically my aircleaner jumps all over the place while idling in park. The engine (idling in park) however appears very smooth and is to the touch also. Inside the car while idling in park it is very smooth as well, just the aircleaner doing its dance under the hood. The metal aircleaner mount is new but I reused the rubber isolators as they looked fine. Holson Adi suggested I replace them as well as he had a similar problem that went away with new isolators (thanks Holson). Everything changes when I put it in gear though. There is a fair amount of engine vibration when idling in gear, D or R. Sort of a "rump-rump-rump" panzer tank quality to the vibration. There is no vibration at all above idle, accelerating or at cruise speeds. I am inclined to think the motor/trans mounts need to be replaced and I will do the rubber aircleaner isolators while I am at it since they are so cheap. Sound like I am on the right track here? I am tempted to adjust the rack damper bolt but I think that maybe should be left as a last resort? Any input appreciated. Thanks, RT

#2 01-12-2003, 04:24 PM

The rack dampener adjustment is so very easy to do, you should probably consider it as the first thing to tackle here. There is a long list of things that can cause what you have decribed, this can be the easiest to solve.
I am not sure replacing those mounts under the air cleaner will improve your problems with the rattles, unless one of them is broke. Then it will rattle loudly. One of the members suggested that he was able to stop the air cleaner from rattling into the valve cover by using an old isolator, and drilling a hole into the left side of the canister about where it rattles into the valve cover. He then just bolted the isolator into the air canister so that it would prevent the canister from stiking the valve cover. I tried that and it works well, and did not cost much.
But first thing there is to check for any broken, torn isolaters.

leathermang · #3 01-12-2003, 04:48 PM

You should check to see if any MB tech bulletins have been issued for you car.... rough idle when old is one I have read about... they have adjustments for that on some of the cars....

psfred · #4 01-12-2003, 07:14 PM

Check the engine mounts. When they get old, they collapse, and allow both excessive movement and the metal insert to bang on the frame under the mount. Usually very much less evident above idle.

5 cylinder (617) engines suffer from a weak spring on the rack that controls fuel delivery, and as they get older, the rack will vibrate for and aft in synch with the engine, leading to serious rough idle that will vanish when the throttle is opened even slightly. Cure is rack pin adjustment, or replacement. The spring will eventually get so bad you will simply have to live with it unless you need to rebuild the pump.

Also, check the valves -- misadjusted or worn valves will cause rough idle from uneven power.

Peter

Holson Adi · #5 01-12-2003, 07:24 PM

Well I'd still replace those rubber mounts as they are really cheap and easy to replace.

Out of the three that I replaced, the one that was soaked in oil was probably the bad one. I replaced two as I couldn't get the other one out until I got a rotary tool. Replacing the two helped a great deal. The one that was stuck was probably still good.

Check under the bracket to see if you have a nut securing the rubber mounts from under the bracket. Mine had those nuts....
Some people don't though...

What kind of vibration are you experience? Is the engine loping from side to side (viewed from the front)?

Maybe it's the rack damper screw. Do you see the idle fluctuating when in gear?

If the rack damper pin is adjusted all the way in it might cause the idle to be rough (the engine rpm fluctuates).

This is all based on my experience... so it might not be the same

Good luck!

rwthomas1 · #6 01-14-2003, 11:28 PM

Replaced engine mounts, airfilter mounts and steering damper today. Aircleaner no longer does its dance. Engine is smooth as silk. No vibration at idle, in gear, at all. Mounts were completely shot-compressed down to nothing. I would like to choke the engineer that designed the driverside mount though. I know you are supposed to remove the engine shock but it it impossible to remove the nut as the shaft keeps turning. holding the shaft is an option but would destroy the shock. I was able to get the job done nonetheless. I would say there is also a 50% reduction in engine NVH while driving as well. One of the cheapest and most rewarding repairs so far. I can't believe how quiet and smooth an 18year old car can be. Thanks for the input. RT

Holson Adi · #7 01-14-2003, 11:38 PM

hehhe glad to hear that!

I remember watching my mechanic do the driver's side mount. He calmly just told me "it's an old design.. and just hasn't been replaced for long.. that's why it's stuck"

I'm sure he wanted to swear hehe..

While at the subject. I am going to try and stick a thick piece of rubber hose between the air cleaner and the engine. I wanna try that and see if I can increase the life of the rubber mounts.

Want to do the 'fourth' air cleaner 'mount' thing.. but I don't feel like drilling through the air filter housing.

BTW, I saw a very perfect 300D Turbo in Anthracite on campus today. I thought it was your car.. upon closer inspection it had a cream interior and MA plates... :p

oh also check this out..
http://www.hatchandsons.com/pages/sales/late_model/RG01

sorry off-topic but at 36,000 mi. it's probably as close as I'll ever get to driving a new W123

psfred · #8 01-15-2003, 01:20 AM

There is a screwdriver slot in the end of the engine shock rod. Too bad it takes a muscleman to hold it AND turn the nut......

I can't wait to get new mounts in both the TE and the 300D -- I suspect the will both be quieter and new mounts will eliminate the excess vibration they both have.... both have in excess of 176,000 miles on them.

i wonder if I should go ahead and replace the tranny mount too!

Peter

mikemover · #9 01-15-2003, 11:13 AM

Quote:

Originally posted by Holson Adi
While at the subject. I am going to try and stick a thick piece of rubber hose between the air cleaner and the engine. I wanna try that and see if I can increase the life of the rubber mounts.

Want to do the 'fourth' air cleaner 'mount' thing.. but I don't feel like drilling through the air filter housing.

There's so much movement there, I seriously doubt if a piece of hose will stay. I posted a long time ago..probably at least a year ago?...about using an old air cleaner mount on the side. It's still working great, no broken mounts, no vibration or noise. Well worth the 10 minutes you'll spend taking it off and drilling the hole!

Mike

rwthomas1 · #10 01-15-2003, 11:24 AM

psfred, no slot on mine! Believe me I would have noticed! I was ready to cut a slot with my Dremel if I couldn't get the mount in but it worked out. Tranny mount is next too. Big difference in steering smoothness too with a new steering damper. Cheap, like $20. RT

Holson Adi · #11 01-16-2003, 12:14 AM

Funny that you started mentioning this, my air cleaner started to rattle and made that annoying metallic rhapsody

whenever I was in gear....

I took the air cleaner off, replaced one that I could feel was the weakest. That took care of it...

Last time I replaced the three with two of the round ones (from Fastlane) and one of the hex-shaped one. The hex shaped one was the thinnest... That was the one I just replaced because it was so weak and tore very easily.

I just ordered some more and will replace the other two...