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2000 SL500 Magma Red Java 2006 Black SL500 2008 White CLK 350
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240 Posts
Discussion Starter #1
1988 560SL. 144,500 miles

For the past few thousand miles the car has been running rough when at idle and also when in drive sitting at a red light or stop sign. Also, sometimes the car would stall when first started, but not again after it ran a few minutes.

The car ran ok when driving, except that if you tried to accelerate at wot from a stop it would bog down bad and then take off.

I just replaced the plugs and wires with bosch and the car is still running rough. There is a noticable difference in how the car runs and definately accelerates better and there is no more bogging down when at wot.

I did notice that when I start the car, it seems like the exhaust smell is pretty lean. The spark plugs were all very white, which I believe is also a sign of running lean.

Any suggestions or ideas why the car is running rough? No vacum leaks indicated by the economy guage and no check engine light.
 

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1978 450SL--117K
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1,374 Posts
Oh boy. not my expertise but here's a few things.

Does it run fine when cold? Might be the WUR, check the encyclopedia for that.

New plugs, are they gapped properly? You have to check them if they are the old style that were recommended for the car.

Fuel pressure?

fuel filters?

Timing chain slop?
 

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2000 SL500 Magma Red Java 2006 Black SL500 2008 White CLK 350
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240 Posts
Discussion Starter #5
I don't have any chain slap at start up, so I don't think it's that.

I've run injector cleaner through and no change and I've run it really hard to get it hot and "blow" everything out. No change.

So i guess I'm going to have to send it to the independent merc garage to have them check it and the mixture.

I'll check back in once it's fixed.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,352 Posts
There is not always a noise associated with TC system failure. At 144K it is over due for guides and the rest unless you have documents showing it was done.
The 560SL does not have a WUR.
 

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2000 SL500 Magma Red Java 2006 Black SL500 2008 White CLK 350
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240 Posts
Discussion Starter #8
The cap and rotor look fine, but I didn't replace those. I should have just ordered them when I did the wires and plugs. I guess that I was being cheap by seeing if the wires and plugs fixed the problem. I should have combined the shipping and been done.
 

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2000 SL500 Magma Red Java 2006 Black SL500 2008 White CLK 350
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240 Posts
Discussion Starter #12
Follow-up

I finally got the car to the indie shop. I explained to them what was going on, what was done and that I wanted it fixed because I'm considering selling the car.

After a week at the shop, the same shop that has always performed great service on the car in the past, I stopped to pick it up.

They let me know that they made a bunch of adjustments on the car, changed the oil and put new exhaust hangers on.

I asked them if they actually found the problem. They said that I probably need to replace the fuel distributor but they adjusted the co2 and air mixture and to just drive it.

I started the car, it still runs rough, but no where near as bad, but now the check engine light is on and it feels like the car has been "dumbed" down.

I asked about the check engine light and they said that since the idle was hunting, they disconnected the o2 sensor and that took care of it but they had to turn the idle up to 1100 rpm's in nuetral or park.

WTH...I asked for this car to be fixed, not to rig it and then be told to just "drive it". I obviously don't want to deal with this shop again. I need to send it to another shop, but at this point I don't even know what to tell another shop. There is no way that I can afford to send it to the dealer right now. I gurantee they'd be in the 4-5K range. Any advice?
 

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Premium Member
1972 280CE
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4,211 Posts
That sucks, please go back to my original suggestion and hone in on the problem cylinder. The easiest thing to do is to crack open the fuel lines coming out of the distributor and then tighten them. The engine should change tone when you do so.

The line that does not cause the engine to change tone is the one with the problem cylinder. You can then hone in to whether it's a fuel, compression or ignition problem.
 

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Previous: 1989 190E 2.6, 1997 E420, 1985 380SL, 1975 450SLC
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747 Posts
Dirty fuel injector(s)? You try any fuel system cleaner/treatment such as Techron?

Does your car have a vacuum gauge like my '85 does? If so, is it behaving properly at idle?
 

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Registered
1979 450 SLC 5.0
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486 Posts
Italian Tune Up!!

I don't have any chain slap at start up, so I don't think it's that.

I've run injector cleaner through and no change and I've run it really hard to get it hot and "blow" everything out. No change.
That's how the Italians tune up Ferraris and Lambos!!! HAHAH!!!

JetPaul:D
 

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1987 560SL, 2000 Kawasaki W650
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1,019 Posts
Could it also be fuel pump assembly issues? I've had intermittent rough idle/stalling at a stop issues.

First thing I did that cured it was a new fuel filter. Lots of crud in the old one, and with the new fuel filter it had more zip as well as no rough idle or stalling.
 

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1987 560SL, 1998 SL500
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464 Posts
My '87 560SL would idle rough everys so often. Sometimes went away when the temp hit 80c. sometimes not. What I did was remove the idle air valve, very easy to do, and clean the sliding valve piston thing with brake cleaner. don't KNOW if that was the problem or coincidence, but now idles smooth as silk at any RPM or engine temp. Since the 560 is semi computer controlled, strange things can affect the fine tuning of the idle circuit.

A good ration of injector cleaner can never hurt, but the air system is just as important. If it runs good at higher RPM and has good power, probably not fuel or ignition related. The idle air system complete with the rubber hoses is more critical at low engine speed I think. All your indie did was treat the symptoms, and never fixed the root cause, I believe.
 

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1982 240D manual 4spd
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42 Posts
Well...my problem is that when the car is first started and the injection pump is on , I am able to rev the engine but as soon as the air pump cuts off then the car would bog down and trying to stall.
If I get it on the road I have to feather the gas pedal in order to pick up speed otherwise it will stall.Once stepped on the gas it would hesitate for about 2 sec and then accelerate.
What could be happening?
I have already changed : fuel pumps,injectors,FP relay,O2 sensor,vacuum lines ,Fuel distributor ( used),put injection cleaner, ran compression test(all cyl excellent).
 
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