Hey guys, a problem has come about on my new w124.
I noticed that at idle it misfires randomly. I assumed it needed a tune up so I replaced
-plugs (copper NGK)
-air filter
-spark plug wires (Bremi)
-cap and rotor(Bosch)
-O2 sensor(Bosch)
But the problem is still there
When I give it gas it’s bucks for a second then moves along just fine, while driving it’s totally smooth. But once I come to a light it starts to buck, oil pressure and tach go down.
Any ideas on where to try next? Vacuum leak? Cam or crank sensor?fuel filter?

Thanks


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1989 Mercedes 260e
1972 GMC shorty van
1982 Harley Davidson Ironhead

I pulled the temp sender out, looks to be original, side note thanks to the engineer who put it that close to the head that was fun to remove, as well as put a bit of dielectric grease in the plugs wires, that seemed to smooth it out a bit, I’ll see on the next drive


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__________________
1989 Mercedes 260e
1972 GMC shorty van
1982 Harley Davidson Ironhead

Vacuum leak? Yes

No cam sensor on M103.

Doubt the temp sender is at fault. I can find a test resistance for you if you want to check it

A clogged fuel filter would show symptoms like hesitation at speed but not idle.

Maybe somebody messed with the mixture adjustment.

Ignition coil and injectors are another possibilities.

Check for vacuum leaks at the air cleaner to valve cover hose, the two hoses at the IAC, the elbow from the intake to the head, the boot under the distributor and the injector seals.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I will check those,
I sprayed a cleaner around the injectors to see if the idle Increased and it didn’t so I think injector seals may be fine, but I will pull the air cleaner and check the idle valve

Thanks you for the recommendations!


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__________________
1989 Mercedes 260e
1972 GMC shorty van
1982 Harley Davidson Ironhead

I know with BMWs the have a plug or paint in the adjustment screw in their early CIS to show if it has been adjusted, I noticed this car the adjustment screw is visible and no paint, maybe someone adjusted instead of a tune up(?)


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__________________
1989 Mercedes 260e
1972 GMC shorty van
1982 Harley Davidson Ironhead

yes there should be a plug blocking that port so somebody clearly adjusted it at some point.


It should be the last thing that people mess with on these cars but whatever.

I assume the NGK plugs you installed are TR5. Those are resistor types. The original Bosch non-resistor H9DCO or H9DC are tough to find. Resistor type plugs cause a slight idle roughness due to misfires and that can also cause an emission test failure. That may be the problem.

It's not a hard misfire that you can really feel - just a slight idle roughness that some might not even notice.

Duke