Glad to hear my cap & rotor were put to good use. For hunting idle, just clean the TPS. Do a search here - basically you spray carb cleaner on it, then WD40 to lube. My 300E had a horrible up/down 500/1500 idle and this solved it. A couple months ago it started to return somewhat, and I cleaned the TPS again and all is smooth as silk once more.

Don't be so quick to replace the injectors. In this order, I would do the following:

1. Run Techron through the tank at 2x the dilution recommended on the bottle. Do this 2 or 3 times, then change the oil.
2. Look for and fix vacuum leaks.
3. Look for and fix injector seal leaks.
4. Inspect ICV hoses and replace if brittle.
5. Clean ICV with carb cleaner, then follow up with WD40.
6. Turn EHA adjustment screw 1/4 turn clockwise - this made an INCREDIBLE difference for me.

That's all I can think of. For the record, my 300E now idles like glass and is a pleasure to drive. I did all the above after idle quality began deteriorating a few months ago. Now that it's fixed, it just sits in the garage and gets waxed every now and then...

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280