1999 SL600: Wandering Idle in Neutral/Park - Mercedes-Benz Forum
 
LinkBack Thread Tools Display Modes
post #1 of 10 (permalink) Old 06-15-2019, 10:12 AM Thread Starter
BenzWorld Member
 
my500benz's Avatar
 
Date registered: Jun 2012
Vehicle: 1999 SL600 (67k miles), 1998 SL500 (sold, owned from 67k-91k miles)
Location: Los Angeles
Posts: 112
Mentioned: 1 Post(s)
Quoted: 29 Post(s)
(Thread Starter)
1999 SL600: Wandering Idle in Neutral/Park

So here's the video:


Not exactly the sewing-machine-smooth idle one hopes to see from the M120. I had a check engine light on for a while; engine was running as well as ever, though. Mechanic said it was for the O2 sensor, but he wasn't convinced that was the problem, so he cleared the light and told me to drive it for a while. I did; it came on again not long thereafter. Took it back this week, he said this time there was a vacuum leak and it needed a new purge valve, which he installed. CEL came back on a few minutes after I drove off. Took it back one more time -- he said there was another vacuum leak and he really fixed it this time.

That's where the video comes in. I haven't seen the CEL come back yet, but there's this new and weird condition where idling in Neutral or Park results in endless convulsions from 700-1400 rpm. If you listen at the tailpipe, it sounds like a misfire on every convulsion at the high rpm point: WHUMP! Drop it into Reverse or Drive and it's steady at the proper 600 rpm point, albeit with a bit more roughness/shakiness than I'm used to.

Any thoughts? I'll be taking the car back in on Monday morning, but if anyone's seen this before, it'd be great to come armed with a theory. Thanks.
my500benz is offline  
Sponsored Links
Advertisement
 
post #2 of 10 (permalink) Old 06-15-2019, 10:26 AM
BenzWorld Veteran
 
FATHERTIME's Avatar
 
Date registered: Aug 2015
Vehicle: 94 SL320 98 SL500 99 SL600
Location: Yorba Linda CA USA
Posts: 731
Mentioned: 2 Post(s)
Quoted: 234 Post(s)
Garage
Quote:
Originally Posted by my500benz View Post
So here's the video:


That's where the video comes in. I haven't seen the CEL come back yet, but there's this new and weird condition where idling in Neutral or Park results in endless convulsions from 700-1400 rpm. If you listen at the tailpipe, it sounds like a misfire on every convulsion at the high rpm point: WHUMP! Drop it into Reverse or Drive and it's steady at the proper 600 rpm point, albeit with a bit more roughness/shakiness than I'm used to.

Any thoughts? I'll be taking the car back in on Monday morning, but if anyone's seen this before, it'd be great to come armed with a theory. Thanks.
Check the large elbows at your MAF's. Mine did this with a loose connection. Also one of them was cracked.

John;
FATHERTIME is offline  
post #3 of 10 (permalink) Old 06-15-2019, 03:14 PM
Outstanding Contributor
 
mahunt's Avatar
 
Date registered: Feb 2008
Vehicle: 1997 SL600 Brilliant Silver Sport with grey/dark metal interior, 234K miles
Location: Lutz, FL
Posts: 1,916
Mentioned: 9 Post(s)
Quoted: 379 Post(s)
Or the MAFs themselves.
mahunt is offline  
Sponsored Links
Advertisement
 
post #4 of 10 (permalink) Old 06-15-2019, 04:16 PM
BenzWorld Veteran
 
FATHERTIME's Avatar
 
Date registered: Aug 2015
Vehicle: 94 SL320 98 SL500 99 SL600
Location: Yorba Linda CA USA
Posts: 731
Mentioned: 2 Post(s)
Quoted: 234 Post(s)
Garage
I think you may invest in a OBDII scanner cause If this guy let a car out of his shop running like that after guessing twice on the two issues that will throw a defined code..........
roadhouse likes this.

John;
FATHERTIME is offline  
post #5 of 10 (permalink) Old 06-16-2019, 03:35 AM
BenzWorld Member
 
BAHRAINI AMG's Avatar
 
Date registered: Oct 2012
Vehicle: 1999 SL500
Location: Bahrain
Posts: 147
Mentioned: 0 Post(s)
Quoted: 40 Post(s)
Tonight I will post a video of how I use my Bosch Actron Scanner (200 bucks) along with the R129 99+ OBD2 cable adapter to scan the codes and clear them too.
FATHERTIME likes this.

2016 Lexus GSF
1999 Mercedes Benz SL500
1993 Dodge Viper RT/10
BAHRAINI AMG is online now  
post #6 of 10 (permalink) Old 06-16-2019, 07:52 AM
BenzWorld Veteran
 
FATHERTIME's Avatar
 
Date registered: Aug 2015
Vehicle: 94 SL320 98 SL500 99 SL600
Location: Yorba Linda CA USA
Posts: 731
Mentioned: 2 Post(s)
Quoted: 234 Post(s)
Garage
I have a 99 SL600 with the same milage as yours and I have never seen another here in in the 3 years I've owned it so a shop that has ever seen one or can work on these is rare. Even at the dealers many have never had one in the shop much less any mechanic that knows how they work. Your car is the best of the SL600 breed as most of the problems they had were worked out by then. I use a shop that has a mechanic does know these cars with all the Mercedes diagnostic equipment. No guess work here. Scanners save $$ plus a cheap Ebay smoke tester is golden for these 20 year old cars.

John;

Last edited by FATHERTIME; 06-16-2019 at 07:59 AM.
FATHERTIME is offline  
post #7 of 10 (permalink) Old 06-16-2019, 10:02 PM Thread Starter
BenzWorld Member
 
my500benz's Avatar
 
Date registered: Jun 2012
Vehicle: 1999 SL600 (67k miles), 1998 SL500 (sold, owned from 67k-91k miles)
Location: Los Angeles
Posts: 112
Mentioned: 1 Post(s)
Quoted: 29 Post(s)
(Thread Starter)
Thanks all. I'll check those connections first and see if they just didn't put everything back together right. It's funny, my mechanic has a sterling reputation in LA for older Mercedes. I've seen more gullwing 300SLs in his shop over the years than I can remember. But the computerized cars make him grumpy, which I'm afraid is what I'm running into here; this is the first computer-y issue my car has had over 3.5 years/12k miles. Will update when I figure it out.
my500benz is offline  
post #8 of 10 (permalink) Old 06-18-2019, 09:49 PM Thread Starter
BenzWorld Member
 
my500benz's Avatar
 
Date registered: Jun 2012
Vehicle: 1999 SL600 (67k miles), 1998 SL500 (sold, owned from 67k-91k miles)
Location: Los Angeles
Posts: 112
Mentioned: 1 Post(s)
Quoted: 29 Post(s)
(Thread Starter)
SOLVED: The new purge valve couldn't really do its job with one of its lines disconnected (see photo). I was poking around in the engine bay per the suggestions in this thread and noticed it. The guy who owns the shop is amazing, but his employees can be hit or miss, and this was an employee job. I brought the car back, they secured the connection with a hose clamp, and the wandering idle was no more. No additional cost to me beyond time and frustration.

P.S. The idle's still not glass-smooth like I'd like it to be, but that's been the case since I bought the car at 55k miles. The tach needle fluctuates ever so slightly, and you can feel the engine kind of fluttering or kicking a little. I'm talking a maximum of 100 rpm either way, but I assume it was rock-steady from the factory with no palpable fluctuation. Would love to bring it back to that spec. I keep thinking ignition coils, but it's never thrown a code for one of those, and in fact the recent CEL was the first one I'd seen in my ownership. Anyway, I'd welcome any thoughts from the V12 veterans on this. Thanks for the helpful feedback on the video.
Attached Thumbnails
Click image for larger version

Name:	disconnect.jpg
Views:	9
Size:	968.0 KB
ID:	2522080  
my500benz is offline  
post #9 of 10 (permalink) Old 06-19-2019, 06:20 AM
Outstanding Contributor
 
mahunt's Avatar
 
Date registered: Feb 2008
Vehicle: 1997 SL600 Brilliant Silver Sport with grey/dark metal interior, 234K miles
Location: Lutz, FL
Posts: 1,916
Mentioned: 9 Post(s)
Quoted: 379 Post(s)
The advertising for AND the smoothness of the V12 is legendary. A quarter should be able to stand on edge with the engine running (really).

Usually a loose MOT valve (you have 2) emits a pretty noisy throbbing sound or hiss.

Time to check ALL the little vacuum connections.

The electronics box at the base of the windshield on the passenger side should have a grey sticker showing the vacuum line routing.

Check all the small black rubber hose vacuum connections by reverse bending and looking for cracks. Check the 3 clear lines that run under the intake for cracks and brittleness. Check the big Z shaped vacuum tube that runs from the passenger front of the manifold near the oil fill, down the spine of the intake (under the black M-B cover) and into the back of the intake close to the master cylinder. Also check the power brake booster engine vacuum line (2 places on the engine).

Don't forget the 2 MAP sensors behind the driver's side front engine beauty cover (they can unplug) and the goofy ERG like vacuum box on the driver's side of the intake just inboard of that side's air box (there's a one way vacuum connection, make sure it works).

Whenever I change out the 3 clear lines (regular maintenance every 6 years), I also check, remove and clean the 2 EGR-like cans that the cross engine clear lines connect to. I unbolt them from the heads and flush them out of carbon grime and check the vacuum elements.

Other than that, make sure your intake elbows don't have cracks or loose connections.
mahunt is offline  
post #10 of 10 (permalink) Old 06-19-2019, 06:24 AM
BenzWorld Veteran
 
FATHERTIME's Avatar
 
Date registered: Aug 2015
Vehicle: 94 SL320 98 SL500 99 SL600
Location: Yorba Linda CA USA
Posts: 731
Mentioned: 2 Post(s)
Quoted: 234 Post(s)
Garage
Quote:
Originally Posted by my500benz View Post
SOLVED:

P.S. The idle's still not glass-smooth like I'd like it to be, but that's been the case since I bought the car at 55k miles. The tach needle fluctuates ever so slightly, and you can feel the engine kind of fluttering or kicking a little. I'm talking a maximum of 100 rpm either way, but I assume it was rock-steady from the factory with no palpable fluctuation. Would love to bring it back to that spec. I keep thinking ignition coils, but it's never thrown a code for one of those, and in fact the recent CEL was the first one I'd seen in my ownership. Anyway, I'd welcome any thoughts from the V12 veterans on this. Thanks for the helpful feedback on the video.
I suspect a vacuum leak, You should get it diagnosed with a smoke tester and with the Star system and a guy that knows how to them it may save you throwing expensive parts at it.

John;

Last edited by FATHERTIME; 06-19-2019 at 06:29 AM.
FATHERTIME is offline  
Sponsored Links
Advertisement
 
Reply

  Mercedes-Benz Forum > Mercedes-Benz Roadster Forums > R129 SL-Class

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Mercedes-Benz Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 

Title goes here

close
video goes here
description goes here. Read Full Story
For the best viewing experience please update your browser to Google Chrome