BenzWorld Junior Member
Date registered: Jul 2007
Mentioned: 0 Post(s)
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420 rough idle, systematic approach and still?
Here's the poop. I have a 86 420sel with 86k original miles. Runs great at 20 mph+. Idles rough BUT occasionally it is smooth as glass but mostly it is not. Hard starting when hot, better when cold.
What I have done.
run 2 cans of techron concentrate
couple of weeks later run 1 can of sea foam
new bremi spark plug wires
new copper core/non-resistor plugs
new fuel filter
new fuel accumulator (definately was bad)
cleaned cold start valve
cleaned idle control valve
fixed 3 vacuum leaks (unplugged hoses) wiggled a million more trying to find a change in the idle.
checked vacuum hg at 20+ on passenger side hose
verified that all spark plug wires are firing at the plugs
cracked the fuel lines on top of the fuel distributor 1 at a time while the engine is running. 5 of the lines drag down the motor as you might expect.
3 of them (cylinders 1, 5 and 6) do nothing when the line is cracked. Soooooo I:
pulled the injectors and checked them.
swapped 1 injector from a known good cylinder (1 that dragged the idle down when cracked) with 1 that did not.
The problem DID NOT move.
The questions are:
How can a rough idle fix itself from time to time for a few minutes while just driving?
Any other ideas about this problem?
Are there fuel distributor rebuild kits out there?
If I pull the fuel distributor off to clean it are there screws, springs, other crap that needs to set a certain way before I put it back?
Can this thing be checked other than that which I have done?
I have the manual on CD, no damn help at all with stuff.
No mercedes joint within 50 miles and local shops don't have the computers to interface with the car.
You concrete ideas are very welcome and if you have something that I do and it works I'll post it immediately so that the plethora of other people with this idle problem will benefit.
Thanks in advance.