560SL Very Bad Idle

My 88 560SL Idles very rough. Took it to my friendly Mech. who told me he thought it was the fuel distributor. Told me he would have to replace the distributor and all of the injectors. Lot of money. However, he told me to try and add injector cleaner over the next month and see if that helped. Has done nothing. It Idles rough but seems to run fine one I kick it. Sometimes it smoothes out for a short period of time but most often it is very rough at idle. I have been reading this forum for some time and have found may discussions about idle but none specific to my car. I have 97K original mile, just had it tuned and do not smell gas in the morning or at any time except after it has been idling for some time.

Because the Mech was not totally sure I am suspect and want to know how I can verify his diagnosis. Also would like to know how I can verify if the distributor is really the problem and not an injector problem.

Thanks for the help

[zla39fj]

Check your motor mounts. They can rough up an idle something fierce and they are very inexpensive to purchase and a DIY project that most people should be able to handle. Do a search on replacing motor mounts.

[JBoggs]

I have posted numerous times with the same problem with my 560sl (also same diagnosis) but no joy so far. I have isolated mine down to one cylinder and an intermittent spark. Tried the Techron cleaner with no luck either. Mine is definitely not motor mounts. My expert mechanic cracked (loosened) the fuel to injector line on the bad cylinder and announced that it was a bad fuel distributor-unfortunately he is most likely right.

I would recommend pulling each spark plug and see if it looks normal (grey on the tip). My bad cylinder plug is coverered with black carbon (unburned gas I'm told). If any of your spark plugs look different (wet or black or broken), change plugs, check wires and/or pull the distributor cap and see if there is any damage or deposits, any cracks or loose wires. You might try running your car with the hood up in total darkness. If you see sparks coming off any of the spark plug wires, you need to replace the wire set.

I hope yours is something simple like a loose or bad wire-I don't think mine is.

Good luck. I'll be watching this post.

J. Boggs

[mhingram]

budlyte,
Replacing the injectors is no big deal 1.5hrs at most easy diy. The fuel distributor is painfully expensive avoid this at all costs.
0. Do this first get the car on a scope and make sure you have a nice firing pattern and have the lamda adjusted to spec. This will tell you if you are burning to much fuel or if the hydro carbons are not where they should be.
1. Check your plugs, wires and distributor.
2. Check all the vacuum lines
3. Check the rubber breathers to the injectors and idle control valve.
4. check your idle control valve
5. check the idle control relay.

Thanks for all the advice. My Mech. said the plugs are all clean, had a tune up about 30 day ago. I suspect that replacing the injectors, a lot less expensive, is something I will try first. If that does not work I guess the distributor is the next step.

Bud

[dmorrison]

Had the same problem. $1100 at the dealer and still does it. Finally had a good mechanic at the dealer look at it. It was the distrubutor cap and rotor.
Remove yours and look at it. If it is corroded or pited replace both the rotor and cap.
I had the dealer refund the $1100 for work that was not needed.

Dave

[JBoggs]

I went the new rotor and distributor cap route since my cap looked suspect and had a hairling crack around the mounting flange. Other than the fact that it starts up beautifully, it still stumbles at idle and at first takeoff once it get warmed up.

I guess I am headed for a fuel distributor after all-but I may try pulling an injector first. Still only appears to be one cylinder missing a little.

J. Boggs

[mhingram]

Sorry to hear it was not the easy fix. Definitely try the injector it cost about $30 with a seal and holder and takes about 15mins to do, very cheap fix.
m

[JBoggs]

How do you tell if the injector is bad? Just replace it? Would it cause the spark to miss if the injector was the problem? I guess what I should do is flip injectors with the next cylinder and see if the problem moves.

I did forget to clean the spark plug after I changed the dist. cap but I doubt it would make that much difference.

And I also noticed the car stumbles a little more at takeoff than before so maybe its fuel pressure related-maybe?

Thanks.

J. Boggs

[mhingram]

J,
If it is pressure check your accumulator bronze coloured metal piece to the lower right of the fuel dist. Make sure it is holding pressure, also check the fuel line pressure coming in to the fuel distributor make sure it is at the spec psi.
Is the rough idle due one particular cylinder, when they changed the plugs was one wet or discoloured compared to the others, try and determine if it is just one cylinder that is causing the problem.

By the way I replaced all my injectors, mounts and seals for $250 in parts and 1.5 hrs of my time. m

Thanks for the update. Just sold my house so I am going to get consumed with moving. Will get to the car as soon as possible. Will check what you suggested and will go ahead and replace the injectors, seals etc. Mech. said that would have to be done even if the distributor is replaced. I just need time.

Bud

[G-Benz]

Vacuum problems can cause a rough idle condition. You may just need to replace the injector seal at the suspect cylinder, and not the whole injector.

If you are going to throw parts at the problem, do the cheap fixes first!