'85 380se rough idle

[barndoor]

my 1985 380se has a rough idle,as if it is "missing"but when I give it gas,it doesn't miss at all.So I dont think it is missing?(spark) Could it be dirty injectors?I have searched this site for an answer,but haven't found one.This seems to be common to this car?or all 126's?.I pulled the "OVP" and re-inserted it.the car sometimes starts right up instantly,other times it takes a few seconds(a little too long)and then seems to smoke (black)on startup.If and when it instantly fires,it doesn't smoke at startup.I replaced the plugs,which had a little more carbon on them than I would like(running rich)I also replaced the cap and rotor.I just recently bought this car and am absolutly in love with it!But I cant stand the car "Rocking" at a stop light!
please help my Benz idle as it should.
thanks!!!,
Mark

'85 380se
'49 vw beetle standard
'49 vw beetle deluxe
'51 vw beetle
'54 vw deluxe microbus
'54 vw standard microbus
'54 deluxe beetle
'67 vw westfalia camper

I'm not a mechanic by any stretch of the imagination, but it sounds as if it might be a fuel problem. Did it start acting up shortly after you purchased gasoline? If so, then I'd guess it's fuel-related. Another possibility is old and failing spark plug wires. Other people visiting this site may have better suggestions. You've asked, and they will come. (I have an '84 380SE, and I love it, too.) Good luck, and I'll be following the responses to your inquiry.

[barndoor]

thanks!
I thought about replacing the plug wires (my next step)
they are 16+ years old,I wonder how long they are considered to last?.I drove the var from so cal with the cheapest gas available.maybe I should start running super?
thanks for the response!

[ymsin]

Plug wires ought to go for about 100k miles before needing replacement. Since your wires are about 15+ years, might just do to have them replaced and see how the idle gets to you. If it still idles, then we might have to look at the idle valve control, or even your fuel mixture ..

One step at a time.

[barndoor]

thanks YM SIN!
you live in the country with my favorite Island
Penang!
great place -great country!
I'll change the plug wires and we'll see
thanks alot!,
Mark

[Aaron]

Mark,

As I keep saying to people, be sure to check that your timing chain hasn't jumped a tooth and therfore retarded the timing to cause the rough idle. I had the same problems with my '85 380SE last year and after long nights in the garage and lots of money spent on overhauling the fuel injection system (fuel head, injectors, etc..) I decided to pull the valve covers (duh!) and sure enough found the chain had jumped a tooth on the right cam gear and that was what caused the rough idle. That week I brought home a new chain, four new rails and a new ORIGINAL Mercedes tensioner (we've seen problems with the Febi-Bilstein ones) and redid everything. Put it back together and VOILA! Smooth as silk! By the way, I did this all at 110K miles. Also switched to Mobil 1 10W-30 synthetic and hopped in the car the next day and cruised down to Atlanta, GA at 85-90mph the whole way. No complaints so far, of course I recently discovered oil leaks from the right head and the rear main! Time to get those jackstands out!

[ymsin]

Aaron - how does the chain jump a tooth?

First time ever hearing of this.

First, if you have platinum plugs in there, get 'em out! Second, check the frequency valve.(if we are talking gasoline engine here)

Third, you may want to go to a shop and have the mixture checked with the CO tester in the tailpipe.

These three things have done it for me the last three times in my 380SL.

Southern Sam: What's wrong with platinum plugs?

Platinum plugs come from racing technology, if you run long distances at high speed they work fine. However, if one stops often and idles while sitting, they soot up. I thought the idea ridiculus until last week. My 380SL would miss after idling for a minute. My mechanic started looking things over and I told him I had just put in new platinum plugs. He immediately raised up, went over to the shelf containing plugs and exclaimed that was the problem. He put in new W8's and sure 'nough, problem cured. I don't know if the new '+ 4' plugs are better, but I think I'll pass from now on. My car, too, was rich and idled black smoke. It needed to be leaned out. FWIW.

[barndoor]

I just put in new Bosch supers.
what do you mean "it needed to be leaned out"?
how did you do this?
mark

Here in TN. we use a tester for emissions. The shop sticks a probe up the exhaust pipe, reads the diagnosis on the machine (computer) and then the mechanic takes a little tool (allen wrench) to adjust the setting through the hole in the middle of the air filter housing. You can see the CO numbers drop as the engine is leaned out (or fuel distributor is adjusted).

Southern Son: Thanks for the information. I hadn't known that about platinum plugs. It sounds as if they're to be avoided. Anyone else want to put in a plug (or "unplug" as the case may be)regarding those things we screw into our engines?

An amendment to my post above; the level of HC (hydrocarbons) should be one of the main factors for leaning of fuel distributor. My 380SL seems to behave best at around 150 to 160 parts of HC. The value of leaning that is best for idle attitude is sometimes referred to as the 'sweet spot'. Don't let someone tell you that to enrichen the distributor adds more power. Better behaved at lean is the better of the two. Besides, there is no such thing as 'power' in my 380SL. I have my '96 LT4 vette for that.

[barndoor]

ok,now the car wont start,and it is stuck at the store!I dont hear any fuel pump noise at all when the key is turned off and on? It sounds like it about to start ,but never does.If anyone knows anything,I sure would appreciate some comments on this one?
thanks,
Mark