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  #1  
Old 08-19-2003, 03:51 PM
larrysiny
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a liitle miss at idle

Hi Everyone,
I hope as usual I might get some answers to a problem I am having with my "86 560SL.The car has 125,000 miles on it and has recently had the following repairs done:
Valve job including all new head parts and rockers plus timing chain etc.
Today I picked the car up from the Mercedes "expert " who replaced the battery, distributor cap, rotor,ignition wire set and ignition coil . I had a minor miss at idle and he said that I probably had original old parts on the car. I picked up the car today andIstill have the miss (the car shakes for a second) then it goes away. This only seems to happen at idle. When I called to complain he said the fuel injectors probably need to be cleaned (around $300) Am I being taken for a ride? What else can I do to solve this problem. I just put a bottle of fuel injector cleaner into the gas.
Any ideas?
Thanks
Larry
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  #2  
Old 08-19-2003, 06:20 PM
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Join Date: Sep 2001
Location: Austin, TX
Posts: 563
For $300, you could buy all the parts to replace the injectors, seals, holders, and o-rings yourself. In fact, $234 from Rusty. The only tools you'll need are a 12mm and 14mm open-end wrench, 10mm socket, probably an extension too, and whatever size Torx bit for the screws holding the fuel injectors brackets (T30?).

Just did this on my M103 engine.
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1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino
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  #3  
Old 08-23-2003, 08:50 AM
Tom McMenamin's Avatar
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Join Date: Aug 2001
Location: Orange Park Florida
Posts: 365
the answer probably is...

vacuum hoses.

I just went thru exactly what you are going thru and after much expense and frustration I replaced any hose that was vacuum and solved this problem once and for all.

The 560 SL is between 14 and 17 years old. These hoses dry rot. Matters not the mileage.

Replace them all and be done with it. It's a cheap fix and worth the time.
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  #4  
Old 10-10-2006, 01:26 PM
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Quote:
Originally Posted by Tom McMenamin View Post
vacuum hoses.

I just went thru exactly what you are going thru and after much expense and frustration I replaced any hose that was vacuum and solved this problem once and for all.

The 560 SL is between 14 and 17 years old. These hoses dry rot. Matters not the mileage.

Replace them all and be done with it. It's a cheap fix and worth the time.

Tom,

Do you by any chance have the vacum hoses part numbers for the ones that you have changed. I plan on changing all of them as you did but not sure which ones should be changed. I just want to do it right and get over with it. I have a 1986 560sl with 120k.

Thank you in advance!

Balsa

Last edited by balsa; 10-10-2006 at 01:32 PM.
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  #5  
Old 10-10-2006, 09:02 PM
79 / 450SL
 
Join Date: Sep 2006
Location: East Texas
Posts: 39
on my 450sl I called German Star and bought 3 meters of each color. I bought 4 and 5 mm sizes and several "Y"s and "X"s. I found 4 mm washer/vacuum hose.
Have fun (beer required).
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  #6  
Old 10-10-2006, 09:49 PM
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Location: Falls Church, VA
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Is your miss at idle "rythmic" - it goes rough for a second or two then recovers with a slight surge in RPM? If so, you may need a new o2 sensor and a mixture adjustment.

If it is more random, then injectors and seals would be a reasonable next step, along with a vacuum line and fitting checkout.

I had a maddening occasional miss that I chased for months and it turned out to be a tiny break in the connector between the intake manifold and the cabin vacuum line.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #7  
Old 10-11-2006, 11:15 AM
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Join Date: Dec 2003
Location: tampa
Posts: 255
Chuck, let me ask you about that. I think that my 88 560SL does the "rythmic" thing you describe. I have followed it using the procedure you described in one of your posts to check the duty cycle and what I see is the duty cycle moving slowly away from 50% percent, rpms increasing, then it correccts itself to around 50% (rpms down) and the cycle repeats itself. It takes about 10 - 20 seconds. I always thought that this was normal. Do I understand you right in that it is not and that I need a new oxigen sensor?

Thanks.

Jl
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  #8  
Old 10-11-2006, 11:55 AM
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Join Date: Mar 2006
Posts: 14
Had something similar happen to my 76 450SL after I replaced all fuel injectors.


All vacum lines replaced last year.


Had a new tune up(plugs, rotor, cap, wires), new fuel distributor, replaced all injectors and then within 100 miles had a miss at idle and when I started to accelerate from idle.

Thinking it could be exhaust, I hollowed out the converters, and put them back on with new exhaust--( had to do exhaust work anyway) problem was still there.

It turned out to be a bit of crud that was loosened when the injectors were replaced. Somewhow it got in one injector. All I had to do was run one bottle of Chevron't techron cleaner through the system.

Problem solved runs like new. That was 5K miles ago, so I know the problem was really solved.

Cheap solution. I woud try that before I got into replacing parts.

Good Luck
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  #9  
Old 10-11-2006, 07:35 PM
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Join Date: Sep 2006
Location: waipahu HI
Posts: 30
similar problem...

I have a similar prob on my 86 300e.
It had sat for a year, broken and when i started it, it fired right up and ran like a tractor. I put in fuel injector cleaner, and started pulling plug wires. To see which ones made the car not run any rougher. Swapped some fuel injectors around and proved it was indeed running on 3. Cleaned them up.. must have been enough.. it keeps getting better and better now. One looked like it had been dunked in an ice cream sunday. Really is a snap to take them off.. But a visual inspection isnt the best way to see if its working.

Best part is, the fuel injectors must have been too dirty for the windows to roll up.. Cleaned the fuel injectors and now the rear pass window is working.
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2003 Mini S
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  #10  
Old 10-11-2006, 10:14 PM
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Location: Falls Church, VA
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No, not normal. These cars will have a perfectly smooth idle if everything is right. I have fixed three cars that were doing this with a new O2 sensor and a slight tweak to the mixture. I t.hink that the sensor gets sluggish as it ages and the computer over-corrects slightly. Try to get the ratio around 45%.

You can get a generic Bosch sensor very inexpensively, and splice it in using the existing sensor's connector.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #11  
Old 10-11-2006, 10:30 PM
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Join Date: Jul 2003
Posts: 528
How do you adjust the idle mixture on a 92 500sl?
I had a rythmic slight rough idle that when I turned the AC on, it went away.
Replaced the O2 sensor with a mustang model, smogged the car and the resulsts were impressive, very clean burning car.
But the slight miss at adle was still there. Last weeekend decided to try to find the problem and stuck a small crewdriver into what I think is the idle adjustment spot, small hole behind the air intake at the fuel distributor area. I pushed down onto what appears to be spring loaded screw and turned it, the car died. Now the idle is smooth. Great result but unsure what I actually did and is not how I like results to come about.

So whereh is the idle adjustment mixture screw located and what is the correct adjustment?
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Thanks, Juan

Last edited by deportes; 10-11-2006 at 10:36 PM.
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  #12  
Old 10-12-2006, 07:37 AM
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Join Date: Apr 2000
Location: Falls Church, VA
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I keep saying this ...

There is no "idle adjustment mixture" on these cars.

You set the mixture at idle, but it affects all driving. It is adjusted through a hole in the air cleaner with a 3 mm hex key while observing the "on/off" ratio on a dwell meter or DMM. The "on/off" refers to commands being sent to the frequency valve which varies the pressure in the fuel distributor by bleeding off small amounts of fuel into the return line. You want to set the mixture so that the current generated by the O2 sensor tells the little computer to send the "on" signal to the valve about 45% of the time. I believe that "on" closes the valve.

Being able to get a good adjustment and a smooth idle around 650 rpm is one of the basic health indicators of these cars. It means that a s-load of stuff is working correctly.

I have no idea what you did if you stuck a screwdriver in the hole. Maybe you were a little rich or lean and you changed the mixture and fixed it. When you make the adjustment, you need to engage the mixture screw with the hex key and gently push it down to adjust it. If you push too much, the engine will stall.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #13  
Old 10-12-2006, 06:52 PM
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Great, I was able to set the mixture at idle as you mentioned and it's idleing a lot smoother. Not sure how it will affect the running at high RPM but it feels a lot better at idle. I was ready to start replacing parts, rotor and caps etc.

great help thanks.
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Thanks, Juan
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  #14  
Old 10-12-2006, 08:01 PM
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Location: S. Texas
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I was stopped once by a little miss at idle and was immediately arrested for solicitation.
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  #15  
Old 10-12-2006, 09:56 PM
79 / 450SL
 
Join Date: Sep 2006
Location: East Texas
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Quote:
Originally Posted by kip Foss View Post
I was stopped once by a little miss at idle and was immediately arrested for solicitation.
Don't cha' just hate it when that happens?
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