1992 400E (124.034)
Okay, fighting an ongoing battle: Rough cold idle/drive/hicupping is an intermittent problem - things are fine on start-up, then when the car drops down to 500rpm things get rough. Goes away after engine warms up briefly, is turned off, left for a bit, but not all day/night and re-started.

Sparkplug wires showed evidence of arcing - which would cause the problem, so I replaced, with no resolution - so a couple of questions:

1. My Premium Bosch wireset (marked for V8 Mercedes) has 11 pieces - Uuuuum, does my car use an 11th wire - if so where? It' the same as the shorter of the two coil wires - am I missing something critical?

2. What other issue would consistently be "resolved" by such a brief, if spasmatic, drive: only several miles, and car usually runs fine when restarted.

3. Finally, despite never having had any warning light (ie..check engine or otherwise), is it likely that a code reader could diagnose this, even if the car is apparently running fine at that moment of the reading?

Vielen Dank, Scotzbenz

Check your distributor caps. There could be some moisture or buildup
that cases miss-fire when cold.

br,
syljua

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1998 CL500 W140
1984 230E W123

Have you cleaned the throttle body (tba)?

Carbon builds up on the back of the plate and interferes with the airflow at idle in particular. You can clean it on the car after pulling the MAF, but is probably best cleaned off the car...

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1994 E420

Thanks, the distributors sound like a must-do anyhow, since I live on the Pacific Coastline and corrosion can be a battle.

I'll likewise do a search here for some "how-to advice", but the throttle body/MAF sort of scares me since I do most of my work when I have a couple hours of free time - and sort of live in fear of disabling my daily driver.

Scotz

make sure you are not fighting harness rot. it started in calender 1992, i think, and continued until sometime in 95. the the engine harness and the throttle body itself can suffer from this. if the main harness is new, that doesn't mean all the little things that have harnesses attached to it were replaced also. just went through this on a client's 95 c220. he had the main harness replaced, i had to replace the throttle body, coil harness and the starter/trans harness. lotsa info here on the site, including the month of production the rotting stuff was installed when the car was built. good luck, chuck.

It sounds like it is time for a major tune up including: spark plugs, spark plug wires (if equipped), fuel injection service, clean the throttle bore, idle air passages and idle air control motor. Also replace the fuel filter and air filter

Scroll down to post #14-#15 in the link below. There is a split of jurisdictions regarding whether you can (should) take the MAF off the car to clean it. http://www.peachparts.com/shopforum/showthread.php?t=220910&highlight=maf+cleaner+radio+shack

If I recall, I was going to clean mine--and even purchased the CRC cleaner--but decided after checking the Lambda that it was okay. Here's the post that may be of interest if you suspect a problem with the MAF or the ETA. http://www.peachparts.com/shopforum/showthread.php?t=202300&highlight=eta+duty+cycle+lambda&page=2

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles