I purchased recently an 88 560SL, a time bubble, 27,500 original miles.
Great car, near brand new condition but a problem has come up.
I am lucky to have one of the best MBZ specialists near me and we have approached the issue in the most conservative and methodical fashion, it is still not completely resolved.
When the air temp is very hot (common here in SoCal) the engine will stumble then eventually stall, it happens almost always near idle or very low RPM, it will restart almost right away in most cases.
All the obvious has been checked, vacuum leaks, fuel pumps, etc... We did the trouble shooting by trial and error testing, replacing the reasonably priced parts and swapping good used parts (the expensive ones) for my original parts and checking for the same symptoms.
We swapped the ECU, ignition CU, coolant temperature feeler.
We replaced with original MBZ parts: the overload relay, fuel pump relay, O2 sensor, fuel filter.
We checked the Air flow mass meter sensor, the readings show a messy signal, we replaced the potentiometer with a new one from a brand new old stock box, it was almost impossible to set correctly and get the car to run right so we put the original back on, we had made reference marks on the housing just in case, it was still tricky to adjust correctly but we got the car to run very nicely, we adjusted the mixture to slightly richer from the adjustment screw inside the tower (tube) that runs all the way up through the air filter. The signal reading is a little better but still not clean but I still think we hit a better sweet spot after we reinstalled the original potentiometer. This afternoon, thinking we had isolated the problem we swapped back to my original ignition CU, within a few blocks after I drove away it stalled 3 times and restarted right away :-( Tomorrow we'll install that used ignition CU back on and try to validate that symptom over the next few days.
I hope I don't need to replace the ICU or the whole air flow mass meter as they are very expensive and this is still an almost new car.
If anyone can add anything to help me out I am all ears, many thanks.

Back in the day. That issue was a common problem.
Does the O2 sensor function correctly?
Does the engine make good vacuum at idle?
Does it happen only in Gear or will it stall in P or N as well?

If it happens in any gear selection either the idle valve OR idle computer is most likely the problem.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

It does it in any gear, the O2 sensor is new and should be fine, this morning I'll ask him about the idle CU and the valve and I'll report here. Thank you for your help.

Latest update
The fuel accumulator is good and I forgot to mention before that we had checked the idle control module and valve and they are fine, so it seems by process of elimination that the culprit is the ignition CU. They are very expensive new and I was wondering if any of you might have a suggestion if and where I can get one rebuilt or find a good used one.
Many thanks

Not sure about the ICU for your 1988 560SL, but when I needed a new ICU for a 1991 300CE I learned that they could not be rebuilt (due to an epoxy over the internal components making it impossible for the rebuilders to identify the components) and none were available used. You might want to contact Beckmann Technologies (800-742-1021) and ask if they have rebuilt ICU's for your car. A new ICU for a 1991 300CE was around $2,500 wholesale ... the owner of the local MB dealer gave me a break on the price because it took their Parts Department so long to locate one for me.

__________________
Fred Hoelzle

You can generally find used EZLs for $100 or so on ebay. There are various part numbers for that part due to supercissions with the oldest EZL being 004 545 55 32, next being 004 545 53 32 and newest being 010 545 67 32. I would try for the newest box. Mark

I just noticed this EZL on ebay for a 560SL.


http://cgi.ebay.com/ebaymotors/MERCEDES-107-560SL-IGNITION-EZL-V-8-1986-87-88-89_W0QQitemZ170381808157QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item27ab8c121d&_trksid=p3911.c0.m14


Mark

Thank you all for all your help.
The EZL or ICU part which is failing intermittently on my car is # 004 545 53 32
Mark, do you think 004 545 67 32 would have the correct mapping for my engine/year?

What happened to the 560SL EZL I linked on ebay? It was for the 560SL. Mark

I don't see a listing for that EZL part number on EPC. Mark

My mistake in the earlier post. The part number for the 3rd version of the EZL is 010 545 67 32, not 004 545 67 32. I just rechecked the part numbers. I apologize for the typo. Anyway, based on the photo the ebay listing is for the second version of the EZL and is the correct EZL for your 560SL. Upon further research, the same EZL appears to be used for all US 560s. Mark

Mark,
Thank you so much for your research, this is very helpful. The EBay listing you linked to is a good deal and has the same part # as mine, I am also tracking a few others and will make a decision very soon, the clarification on the latest part #'s for US 560SL models is great too so it sounds like I'll stick with part # 004 545 53 32.