M116 380 engine surging
 

This is not my car, this is my aunt's 83 380SEL with only a little over 100,000 miles on the clock. It is surging....mainly or at its worst when cold, but it also when it's hot. Any ideas??

TTT

Clean the idle motor/valve, if that dosen't work upplug the idle speed control unit, it should settle in around 1100 in nuetral.



Joe

Thanks Joe. Do you mean the idle control valve? What does unplugging the idle speed control unit supposed to do (as far as fixing the surging), and where it is located? Or is this the same thing as the icv?

Well I've done a little tinkering and this is what I have so far. I cleaned the idle control valve, and it made it idle up much quicker when unplugged, but doesn't make any difference when it's plugged in. When cold (and plugged in), it does not idle up much at all, and the idle is really lumpy. When I unplug it (cold) it idles up where it's supposed to be and runs smooth as can be. As soon as I plug it back in, it stumbles really bad and acts like it's gonna die but doesn't. So is this a simple bad idle control valve?? Or could the problem be somewhere else which is affecting the ICV? Where does that plug on the front of the ICV originate? Could where that signal or current originates not be getting to the ICV? How can I test all this?

TTT

Been there, done that ...
 

The trouble with this sort of problem is that it could be one of about ten things wrong, and maybe even a combination. And without some serious diagnostic tools, you are kind of stuck throwing parts at it.

Given your symptoms, if it were my car, here is what I would suspect:

- vacuum leak at injector seal or manifold causing lean misfire

- bad injector(s) leaking or not opening at idle causing either rich or lean misfire.

So, I would see if Auntie would pop for a new set of injectors and seals - about $220. A very enjoyable wrench for you. Even if this does not fix the problem, it will eliminate a likely cause, probably make the car run better, and the injectors and seals will be good for another 100K.

You can do the injectors one at a time, and while you have one out, run the pump to purge the line and get any crap out of it.

After that, if it still misses, I would start looking into the electronics.

All IMHO.