Hey guys,
I've got an 86 300sdl with >250k miles. The car was well maintained and runs well with good power and no blowby. The trouble is with the idle, or eds... At any engine temperature if I raise the engine speed and let off of the throttle abruptly, the engine speed drops so low the belt squeaks and the engine nears stall for an instant, then the eds begins to bring the idle up to the correct level. The whole process takes about 3 seconds between throttle release and recovery. The tach works consistantly, the abs light never come on and the a/c works properly. Other things to note... changing the idle knob position makes no difference in engine speed, and pulling off the plug on the back of the ip results in a drop in engine speed which resolves upon plugging the ip back in.
I dont know much about the eds on these cars, and i have diagnosed it based on the info i have gathered from this forum.... with no luck. Any help would be appreciated!

My ELR control unit up near the firewall does change the RPM as it is supposed to. However, I've got two odd idle behaviors that I have never been able to explain. I'm going to add these details in the hope that something useful comes up between them.

First of all... I have actually had the SDL completely stall out on me under the circumstances you describe. It ONLY happens on extremely hot days after long hard hot drives. Under those conditions, if I rev the engine to 2500 or higher (give or take, i've had it happen at lower speeds too) and then take my foot away abruptly, the engine rpm drops like a rock. Sometimes, it catches and "shudders" at about 450 or 500 rpm for a second or two and then recovers, but more often than not the engine completely dies and I have to restart. This is particularly annoying on stop-and-go interstate conditions, having the engine die as soon as I move up one car length. It seemed to get a little better when I replaced the defective fan clutch, but then the symptom has occurred again even with a functioning cooling system.

Secondly, also possibly related, completely unconnected from how long the car's been running or how warm the engine is, occasionally my idle will randomly creep up to 900 or 1000 for 30 or 40 seconds and then just as randomly settle right back down to where it's supposed to be.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

So, my sdl also occasionally has this condition that you mention with regard to the idle of about 1000 and slowly creeping down to normal. This seems to happen randomly while driving, with no noticiable precipitating factors. I think what I might do is consult the dealer... perhaps i can find and talk to a sharp mechanic that has experienced a condition such as this. It's really frustrating!!!

read the post a few up about "a safe way to increase idle speed", it looks pretty grim for us!!

My SDL does idle drop too as well as the idle creep up....I just live with it....

__________________
91 350SD
14 F150 Eco
19 Fusion Hybrid
11 GT500