300E 2.8 cold starts with high RPM - Mercedes-Benz Forum
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post #1 of 12 (permalink) Old 04-04-2019, 11:30 AM Thread Starter
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300E 2.8 cold starts with high RPM

I have a 1993 300E 2.8 with 83k miles and was starting correctly the past five years I've owned it. Recently I did a big job of replacing the U-seal for the timing chain cover along with, the fan clutch, thermostat, removed throttle body to thoroughly clean, replaced all coolant hoses, timing chain tensioner, spark plugs (old ones i had were bosch 7927 which my car seemed to love but switched to Bosch F8DC4 since i believe is what everyone says are the correct plugs), Bosch coils, kingsborne spark plug wire and boot set, new OVP, new Bosch MAF, lower wiring harness, new Bosch fuel pumps and fuel filter. It already has the updated upper wiring harness. So after the two month job with countless hours, the car now cold starts with a noticeably high rpm at 2100 as if i tapped on the throttle but immediately smooths out to correct warming up rpms. No codes either... I have an updated Bosch O2 sensor coming in since it still has the original one but I doubt that's the reason. I'm guessing it could be the throttle linkage adjustment, the new spark plugs or I incorrectly connected the harness or a vacuum line. Thanks!
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post #2 of 12 (permalink) Old 04-04-2019, 11:36 AM
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The throttle body is made from the same eco junk wiring as the harness.

If it is still original, high likelihood that is the culprit.

FWIW, the idle is non adjustable due to being under computer control.

Also kingsborne plug wires isn't what you should use.
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post #3 of 12 (permalink) Old 04-04-2019, 11:45 AM Thread Starter
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Thanks for the right direction! Guess i need to check the insulation out. Any idea what available brand spark plug wire set I should be using?
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post #4 of 12 (permalink) Old 04-04-2019, 11:52 AM
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One of the 3 Bs (Bosch, Beru or Bremi). Ditto using the boots from one of the 3 Bs. These cars not forgiving when it comes to ignition parts.

No need to check the insulation. Check the tag for the fab date xxMxx. Anything made prior to 1998 is eco junk. If the label is washed, it is eco junk by default

And always replace the throttle body gasket whenever the throttle body is removed to avoid having a high idle due to vacuum leaks. The Mercedes gasket is very inexpensive. No need to go bottom dollar on this part.
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post #5 of 12 (permalink) Old 04-04-2019, 12:24 PM Thread Starter
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Guess I need to do more ebay searches for a set. If it's eco junk I'll just have a rewiring job to do. Thanks again! For now I'll switch over to my old wire set and see if there's a difference.
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post #6 of 12 (permalink) Old 04-04-2019, 12:37 PM
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FYI, I've never seen a rewired throttle body go the long haul. If you want it to last, your best option is to find a non eco junk era (1998 and up) unit
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post #7 of 12 (permalink) Old 04-04-2019, 12:37 PM
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Originally Posted by VAHAG View Post
Guess I need to do more ebay searches for a set. If it's eco junk I'll just have a rewiring job to do. Thanks again! For now I'll switch over to my old wire set and see if there's a difference.
Don't worry about the ignition wires for now. They'll work just fine for awhile. As mentioned, the throttle actuator is a prime suspect for what you've described.

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post #8 of 12 (permalink) Old 04-04-2019, 12:39 PM
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Also keep in mind that your engine uses a disposable ignition system. The average lifespan of the wires, coils, and plug boots is about 150K miles or 10 years.

Plugs need to be replaced about every 25-30K miles.
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post #9 of 12 (permalink) Old 04-04-2019, 01:18 PM Thread Starter
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I'll be on the look out for a throttle then. I'll report back once I check out the date and some other basics. Still proud it showed up after 26 years.
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post #10 of 12 (permalink) Old 04-04-2019, 01:22 PM Thread Starter
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Originally Posted by sbaert View Post
Also keep in mind that your engine uses a disposable ignition system. The average lifespan of the wires, coils, and plug boots is about 150K miles or 10 years.

Plugs need to be replaced about every 25-30K miles.
Guess i was due for a new complete ignition set 16 years ago
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