ENGINE REVS WHEN IN PARK AND NEUTRAL

[450se1979]

@TJ-450

It is oscilating but only when idling.
When revving the engine, it dissapears.....
It is not misfiring, the plugs are ok, no build-up whatsoever.
If it would be bad plugs or plugwires I would have at least some discolouration.
Both heve been replaced, original Beru plugwires, Halo plugs, new distributercap an rotor.
If the mechanical injection is at fault  there would be a loss of power...
Ik replaced the injector seats and grommets and cleaned the injectors, no help.
I suspected the fuelpump but when revving it shows plenty of pressure.
Besides running the car on petrol, its runs on LPG, no problem with oscilating!!
I don't consider the oscilating as being disturbing, but it just doesn't feel right with such a wonderfull automobile.


Jeen

[CraigS]

I haven't read through all of this thread, but have you checked the return fuel line ? Might be an idea to open it up and blow some compressed air through it. There is also a "coil" in the bottom of the tank (that is all but impossible to get to - you can see it if you look through the sender unit opening). That can get blocked as it is a minute opening. Only way to clean it is to remove the return line and use some thin wire to run through it, then some compressed air. Obviously the tank needs to be empty. It doesn't really help to remove the tank - other than making it a little easier to work on it.

[koan]

I seem to be having the same problem on a K-Jet engine; is there a different fix for the K-Jet?
The fluctuations in at idle speed are appr 300rpms, but are very consistent...

I've heard petrol engines idle with a lope when they have big knobby lobed cams (brump, brump, brump) but unless you're not telling us something its not going to be that. Don't know if advancing cam timing has the same effect, someone may have tried to compensate for chain stretch by advancing the cam a tooth.

The only other possibility I can think of is some vacuum problem with ignition advance. Try removing the vacuum advance from the distributor and block the line off, see if it idles any better. If the idle changes is any way with the vacuum off it indicates something is amiss somewhere.

Check the vacuum connection(s) to the distributor, there should be a diagram in the library.

koan

[JAYAUCK25]

Many thanks to oscar for presenting the solution this problem!!!!  Works great now.

[oscar]

Fantastic Jay   I've gotta give credit where credit's due and I've basically repeated things that were told to me by a fella named Greg on the aussie MB club site a few years ago, plus some extra bits of info from a few others I can't remember, but it fixed my issue and glad it's worked on yours too.