Mercedes-Benz Forum banner

W220 Engine Vibration @ Cold Idle Only

15K views 11 replies 4 participants last post by  Quadcammer 
#1 ·
Greetings all,

Longtime lurker, first time poster. Bought my 2000 S500 new, now has 69,000 miles, dealer serviced regularly...last several years have not driven it much, maybe 2,000 miles/year.

Have been to the local dealer multiple times with this issue that started a couple of months ago: Upon starting the car cold, there is fairly significant vibration felt through the driver's seat...the vibration vanishes after the revs fall and the engine drops to "slow" idle. The car is otherwise performing perfectly, both around town and on the freeway.

The dealer's first guess was motor mounts and/or a fuel system issue. Motor and tranny mounts were replaced three years ago...but they did find one of the motor mounts was starting to crack, but no failure...all other mounts were OK...and the fuel system was OK. I didn't ask them to replace the one motor mount under the assumption that if it really was the motor mount, I would feel the vibration at idle all the time...not just when cold.

After much research on Benzworld, I went back and asked them to check the harmonic balancer...which actually looked as though it was wobbling a bit...verdict was the HB was fine as was the belt, but the tensioner needed replacing...$500 bucks

Now, it seems that the vibration is worse! Still vanishes after the initial "fast" idle...and the car is vibration free after warm (both @ stop lights and after warm starts)...

Brought it back...their new theory (after the "shop foreman" did a cold start this morning) is that there is a failing Air injection pump...not sure if I see the logic, but I suppose its possible, my SA suggested that @ start the pump is working harder...and the "shop foreman" felt the pump vibrating when they did the cold start.

Sorry for the lengthy post...but would really appreciate any help and/or suggestions..

Many thanks.
 
See less See more
#2 · (Edited)
I just went through the same thing. I gradually saw my gas mileage get worse and worse over the next few months and was wondering what was going on. Also power and throttle response was getting worse accordingly. Idle was good most of the time but was tempermental. Some days was perfect and some days you would feel a miss. I replaced a bunch of things as well including the harmonic balancer. Before you do anything else check the resistance of the spark plug wires to make sure they are good. Even though my wires and plugs were just changed 20k miles ago, I didn't realize that the resistance was all over the place until it was checked with an Ohm meter. Ebay sells a set of 16 Bosch wires for $170.00 shipped. At first I thought it was a weak coil. What is strange is that my slight misfires did not cause a check engine light to pop up. Your tech is full of sh%$ to say it is your air injection pump. That has nothing to do with cold idle. Get back to the basics. Good luck.

Oh btw I also changed my motor and tranny mounts did not change a thing.
 
#3 ·
nice, thanks for the quick reply...

I just drove the wife to the airport...same stuff: Cold start, rough "high" idle (with vibration felt in the cabin) for about 5-10 seconds and then smooth "low" idle...and no issues idling in stop and go traffic...or on warm re-starts. I saw that you had some power loss and poor mileage...and, as of yet, I haven't had that...mileage seems pretty consistent and power delivery is smooth...

Will definitely have them check plugs and wires...yeah, as I said, I'm skeptical about the air injector pump theory too...but my SA suggested I leave the car overnight and go over first thing tomorrow and start the car up with the "shop foreman" present...and let him prove to me that its the pump...

Oh yeah, forgot to mention that my HB was replaced in '05 when they did the recall/campaign, so it has been replaced once already...
 
#5 ·
I was chasing a very similar problem like that for some time, did plugs, wires, mounts, filters, etc.

Three trips the dealer until they finally spent time diagnosing the harmonic balancer. Even though mine was already replaced by the original recall, that was the culprit. They originally thought it was the exhaust needing to be retensioned after the new mounts were done. They at least credited me all the original diagnostic work.

When cold and you rev and hold at around 1200-1600 rpm, is that when you feel it? That's what mine did.

Hope that helps!

P.S. mine is a 2000 S500 with 117K on it.
 
#6 ·
Oliver & dmarti, thanks for the replies...

So I just dropped off the car at the dealership (again)...spoke to the "shop foreman" (who was very nice and seemed to know what he was talking about...but lacked a bit of credibility because he was dressed in a starched, button-down oxford shirt and slacks...would have been more impressed had he been in greasy overalls)...and we agreed I would go back tomorrow morning and have him start the car cold while sitting in the driver's seat...

The foreman told me that when he started it yesterday morning he heard a strange noise and vibration from the Secondary Air Injector...and therefore he thought it was the culprit...I'm still skeptical, but his point was the SAI works hardest when cold so as to get the engine and catalysts in the CC up to temperature...I responded saying it seemed implausible that such a small part could cause a vibration I could feel in the seat on the cockpit...we then discussed motor mounts...and our agreement was that they would recheck the (3 year old) motor mounts after our cold start test. He confirmed that they previously pulled the harmonic balancer and checked it and the belts and they were all OK. I didn't bring up the plugs and wires yet, but will if it turns out the motor mounts are still OK.

Will report back tomorrow morning...thanks everyone!

PS. dmarti, many thanks for your posts on your vibration saga...it was what caused me to think about the harmonic balancer, even though I knew mine had been replaced...I'm just hoping my tale won't take a year :)
 
#7 ·
So after having left my car at the dealer for two days, good news and bad news.

Good news is (i) not one, but two shop foremen (along with my service advisor) confirm that they feel the vibration upon cold startup (and that the vibration disappears upon dropping to slow idle)...and that the vibration is unusual (ii) shop foreman #1 has acknowledged it isn't the Secondary Air Injector, (iii) both shop foreman thought motor mounts were the most likely culprit, (iv) I've been reassured that its unlikely something catastrophic is brewing and (v) they didn't charge me anything since there was no diagnosis.

Bad news is (i) Both shop foremen and my SA think despite some small cracking in the left motor mount (right motor mount and tranny mount OK), its highly unlikely that is the cause of the "cold idle" vibration and, bottom line, (ii) no one has any other guesses as to what it might be.

And to nice & Oliver points, I did ask multiple times about plugs & wires and was told that either (i) they'd see a code and/or CEL or (ii) the vibration would happen at times other than at cold idle.

So, unless someone else has another theory, I just might have to live with it...though if I have the time, I might bring it to the indie mechanic that works on my wife's 300D...

I'm in the West LA area in case any of you might have an incredibly good and intellectually curious MB mechanic that likes solving mysteries...

Thanks again for the input..and please, if anyone has any other ideas, please speak up :thumbsup:
 
#8 ·
are you mechanically inclined at all?

If so, I've found that I don't mind throwing parts at the car if they are inexpensive.

For instance, my plug wires are likely fine, but for about the cost of one hour of dealer labor, I'll eliminate that variable and end up with new parts.

Its not the best way to go about it, but throwing parts combined with some educated guesses seems to work out fairly well.

This really only works though if you're able to do your own work.
 
#9 ·
Hey Oliver, thanks for the reply

I kind of do that on my wife's 300D...I do a little of it myself, but usually just buy the parts @ autohauz and then bring it over to that indie mechanic I mentioned and have him do the parts exchange.

Haven't done that yet with the S500...since I really haven't had to (though I did get an indie guy to replace the airmatic pump & relay when it went out a couple of years ago)...but if the problem continues into the spring (as it gets warmer) and/or gets worse, I think I will follow yours and nice's suggestion and replace plugs and wires...

Hopefully the two MB shop foremen were right and that nothing really bad is going on...
 
#10 ·
i really doubt its anything major or it would let you know.

Just did the plug wires. If you want to do it yourself, my only tips are to remove the coil pack bolts (no need to unplug from harness) to make things easier. Next, plug the wire into the coil first, then the plug. Start from the back and work forward, doing one at a time. There are like 4 part numbers, so you don't want to get them confused. Finally, use some dialectric grease on the plug boot. I did that when i did plugs about 3 years ago, and the old wires came off by hand very easily.

My idle, while always quite smooth, seemed even better now, with basically no shivers at idle. Again, not a huge difference, but its not like this thing shakes like a funny car. At the price, I'm glad its done.
 
#11 ·
Hey Oliver, thanks for the reply...

Yeah, I'm most concerned with the catastrophic failure (eg., harmonic balancer blowout on freeway)...and as long as this isn't a symptom of something major, I'm a bit more relaxed about it..esp. since I don't drive the car that much. My wife thinks I'm getting a bit psycho about it...given her W123 almost shakes like a funny car ;)

I did, however, notice one thing yesterday night...I was messing around with the climate control and turned the CC off (the "0" setting)...and noticed the idle was completely silent, also had the radio off...and when I turned the CC back on, felt a vibration similar to what I had experienced during the cold idle...haven't done an experiment to try a cold start with CC off yet, but now am wondering if there might be some issue with the A/C compressor (or some other CC part) coming on...because the vibration was similar, though less pronounced...

Have you (or anyone) had any unusual vibration symptoms before something in your A/C system went out?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top