gp.palmonka

Hi, my 1986 560 SL has good running days and bad runningdays. It has 132K + miles but the odometer was broken when I got it. Sometimes it runswell and sometimes it runs rough andstalls. It always idles a little rough like it may have a vacuum leak. In idle,the speed is always surging or hunting. I’m in Florida and it is never drivenin cold weather.

It has new fuel pumps, fuel filter, check valve, accumulatorand fuel distributer. Fuel injectors have been removed and tested and all areclear and open at specified pressure (about 60 psig). I have cleaned the idlecontrol valve with carburetor cleaner and have added BG - 44 K to the fuel. I have replaced all of the injector seals, injectornozzle holders, and engine air distribution hoses but it appears to have avacuum leak that I cannot find.

When it is running rough during driving, it starts to stallwhen decelerating but usually catches and idles roughly. Twice it has stalledand would not start. After waiting 10 to 30 minutes it would start and runrough.

The last time the engine stalled when stopped and waiting toturn into traffic. It would turnover and begin to fire then stall whenreleasing the key. After about 30 minutes of intermittent attempts I changedthe fuel pump relay. I had replaced the fuel pump relay as maybe that was one of theproblems and still had the old one in the car. There was no obvious difference afterchanging to the old relay but after repeated attempts to start the engine itfinally caught. I had to apply additional throttle to keep the revs up to about2000 keep from stalling. After about 5 minutes of running at higher idle I wasable to step off the throttle and the engine would idle roughly. When drivingit home I had to keep on the gas when slowing down to stop by putting it inneutral to keep the revs up to keep it from stalling.
Some days it runs great with no problems to drive to localshops about 3-4 miles away.
Then when returning home the same 3-4 miles it runs rough and barely keeps fromstalling.
Sometimes it’s the other way around and it runs rough out of the garage andsmooth on the trip home.

I don’t take it on any long drives or go far from home withit as it may be one of those “bad” running days and I’ll be left stranded. So Ican’t get any continuous highway miles of running time.
Any suggestions on what to check next would be greatlyappreciated.

Thank you.

seandedrickson

Had the same problem with my 87 560 SL. Finally took it to the dealer and they adjusted the fuel mix - solved. Was running rich and flooding out. I'm told there is a science to getting this right on this car and not many people are able to get it right.

vin142

i had the same problem and found the distributer cap and rotor both broken, you dont say if you changed out those parts but it cured my problem when i changed them out.

kennedy759

my 88 did some of the same, replace temp sensor and fixed it.

vin142

my 89 560 sl had the same problem. i found the distributer cap was actually broken, it fell apart when i took it off. the rotor was broken also. after they were changed out that problem went away. it still missed and changing the wires cured that.

slik560

Also could be ICM or crank sensor -extreme cases, but sometimes they do go bad. Every time I think I get things fixed, something ELSE comes up. Love the car, but the unreliable nature keeps me from going any distance from home.