1989 300SE Slight misfire at idle diagnosis

Just checking that I've made the right diagnosis. I've got a slight intermittent misfire at idle on my 300SE. Should I change the rubber seating seals on the injectors, or should I
consider a full set of new injectors, since the ones installed have done maybe 150k miles? Also, are there O-rings on the plastic injector holders/insulators, and should I change those too?.
Cheers... Rob.
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Hi Rob,
So you went for the big new car!
You've checked the ignition wires' ohm resistance?? (Easier than attacking the injectors.)
Good distributor cap and rotors?
Have you checked for an intake manifold gasket vacuum leak?
Finally, injectors can be professionally ultrasonically cleaned, flow tested and leak checked for about $20 each - if it comes to dealing with injectors.
Hope this helps you find the cause.
Tom
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Hello Tom Well, I turned 40 didn't I. I'd got all the permission slips from wifey. Gave my trusty 123 280E to a good home, and managed to give my Russian Lada Niva jeep away too! (I seem to have given 4 vehicles away over the last few years, all of which are still going strong. Gotta say a friend o mine has already put his name down for this new gentleman's carriage). I was all set, and I'd asked a couple of Q's here (you responded as always [thanks] ) and calmed me down from a star ship miles V8 I was looking at thru rose tints on Ebay. It had to be the S class Panzerwagen!
Anyway, a local guy had been reading my posts (here) and out of the blue offered me his 2 owner (him since 1990) from new 1989 300SE. I reckon the 6 cylinders is enough for me. I'm not a speed merchant (or refinery owner). Its a straight car, with no air-con or other tricks. It has got a sunroof, always a liability on an older car, but there you go. Its about as simple as a big complicated car like this can get. Anyway, to cut a long story, I looked at it (and so did wifey!) and bought it. Its nice, light met blue and its had pretty much everything looked after by an aftermarket Merc place all its life. Got a good service history and even the two cards that came with the car from the factory with all the data on. Anyway, I got the small bits and bobs of corrosion sorted on the extremeties of the front wheel arch and a little appearing from behind the plastic trims on the front doors. My mate who does the bodywork reckons that the plastic trims they put on so many cars nowadays, cause the corrosion over the years, since they tend to chatter a little in the airflow as the car moves, so they kind of rub through the paint and hey presto. Corrosion. Niggles so far are that it failed to start on me once, but I blame the immobiliser for that (got this fancy cat 1 immobiliser that cuts off all sorts of things. Never trusted em, especially when you didn't fit them) There is a slight external coolant leak from somewhere I haven't traced yet, but when you open the hood after a run, there is a definite warm water smell towards the front, but nothing to see. Its also got a slight intermittent falter at idle, which is why I rushed here for advice. I understand that the injectors could be cleaned, but I can get a full new set on ebay at the mo for $20 each, so I was tempted. I mean, these things have a spring (pintle?) valve inside them. Doesn't that valve wear over 100k miles?. Anyway, I'd read lots (here again) about the rubber seats and O ring on the plastic seatings that age and can cause air leaks, so I was going to change those if it was prudent (and they are cheap to buy).
I haven't checked anything else yet. HT leads.. Are they carbon?. Why don't we use copper anymore, with suppressed ends?. It was easier to check the connections. My Ro80 has all copper with the original suppressed ends. With the lethal BOSCH CD ignition system on it, it destroys the carbon leads in less than 1000 miles. I've seen it draw a 1 inch arc out the side of one in the dark during engine cranking. Very impressive, but no good for smooth running. My old boss was right I guess. There's no such thing as an open circuit for HT!. I guess I'm looking for less than 50k Ohms on a lead?
I'll look at the dizzy cap and the rotor arm.
Any tips for an easy way to check the intake manifold gasket?. Is 'easy start' good for that (similar to the leaky injector rubbers)?
So... There we are. I've plunged,.. now to make it perfect.
Thanks again Tom
Cheers... Rob.

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Rob, sounds like a good machine; I've always liked the look and size of the SWB S Class and thought of buying one some time ago.
I suggest you simply compare each ignition wire's ohms vs. its peers - if there's a fault you'll soon find it.
Yes, carb cleaner, starting fluid or propane will be pulled into the motor by a vacuum leak - be it at an injector seal or manifold gasket. Of course keep your face away from the test site - even if gets interesting!
Good luck with the 300SE!
Tom
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Cheers Tom.
we've had a major extension on our house over the last 12 months, which is now in its final throws, which means we are currently waiting for my new fancy pressed concrete drive to set hard. The minute its gone off, I'm on it and under the hood with the meter and the gas. They say you should never trust an engineer with no eybrows!
... Rob.

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