300E idle speed adjustment?

[Ron Miller]

Hello:

I have a 1986 300E that is my first Benz, and I have owned it for a little over a month now. My idle speed seems to run a constant 1300 rpm with the engine either cold or hot. Is there any mechanical adjustment of the idle speed? Or any other kind of adjustment of the idle speed? Thanks.

I'm not a tech and don't even want to take a stab at it.

However, since we're on the topic of idle I'd like to add an additional question here regarding idle on my 93 190 2.6:

At certain times, upon startup only, my idle will race up to 1300 or even 2200rpm and refuse to settle back until I start driving. This *only* happens when the car is warm and has been:
1) at elevated highway speeds for long period of time then shut down and re-started after a short duration (ie: fueling), or
2) if I'm re-starting (warm) after failing to fire it on the first attempt (read: let go of key too early and it died).

It's also stumbling on starter-power a little more before cleanly firing on warm starts, if that matters...

Keep in mind that this occurs infrequently after highway trips and occurs far more under scenario #2 above. Goosing the throttle rarely if ever helps re-set the idle. Only after shifting into gear and driving 1/4 mile or so will it re-adjust. I have no idea what may be causing this, besides possibly the O2 sensor or *shudder* the idle speed computer (doesn't that cost like $1700?!). My 90k service is coming up but I'd appreciate some help from those interested/knowledgeable about idle issues. Oh yeah - and it IS becoming more frequent. Ideas?

Best,
Matt

[Ron Miller]

I did some reading, and somewhere it said in park or
neutral trans position, there is a ground circuit that has to be there for
proper engine idle operation. I find my car will start in any gear!! Where is
the switch for the park/neutral position? Also, I find a little vacuum line
broken that comes from the pcv hose on top of the engine ( this black rubber
hose has a little manifold to adapt to the little hose size and goes from
the valve cover to the air cleaner cover) and runs down to around the "carb"
area. I would suppose this may have something to do with idle speed too?
Also, I checked the over voltage relay and it appears to be ok, and the fuse
is ok. I pulled the conn block of of the cis unit and checked the voltage
there according to my manual. Voltages there appear normal so far. Is all
this a big problem or can I dig in and do it myself?
Thanks.

[Benzmac]

Any vacuum leaks can cause a high idle. I would repair the vacuum leaks, then check to see where the idle is.


As for the Makakio, it would be easy to check this if the problem was happening. You will have to find a tech to look at it at the time of the failure.

Thanks Donnie - having it checked when-occurring is always the difficult part, no?

[Ashman]

Makakio,

I had a similar problem with my jeep. i would start it and it would go up to high revs and wouldn't come down at all sometimes.

I had to have something called the idle speed sensor or something like that replaced. or The Idle Control valve not sure what it was,but since i had that part replaced the car never did it again.

If you can start your car when its in gear, then most likely the the Neutral Safety switch has a problem.

Some cars may not have this feature, but i would assume most cars do.

P.S. i'm not a tech, but just thought this would assist because of the similarity of the problem even though in my case it applied to a jeep and not a benz.

Alon