380SL rough at start? Help!

When I start my 380SL when I first start it it runs rough, then when it warms up it goes away. The idle with AC and in drive is ar 600, any suggestions...

[iwannabenz]

Hi all, I saw this post in the tech help forum, no replies there, any help here?

My (very) recently acquired '85 380SL has EXACTLY the same problem. It starts on the very first crank, but runs extremely rough. Ambient temperature is approx 5C, or 40-45F. As it warms up, it begins to smooth out. When full operating temperature is reached (15+ mins idling), the rough running is completely gone, and it runs quite smoothly. Plugs, distributor cap and rotor have just been replaced, and my new baby has been pampered from birth, with only 128,000 kms(80,000 miles). In a quite extensive search of this excellent site, there have been several conflicting answers to this type of question, in particular regarding the O2 sensor. Some suggest this is the culprit, while others say the O2 sensor has no bearing on engine performance until it is warmed up. Other possibilities center around the warm-up regulator, which is (for me) a very scary expensive part. Any ideas? Am I missing any input variables? thanks.

[The Black Guy]

Thinking out loud, Could possibly be catalytic converter. Once the car warms, the exhaust flows more smoothly.

Just a thought.

[iwannabenz]

Wow, I never thought of THAT, so what do we do, put a pre-heater in the catalytic converter? Has anyone ever done this? Does Mercedes have a part number for it? Would it be electric or gas-powered? Any other ideas out there?

[diggad]

A friend with a 380sl swore that he had the same problem, and said it was due to the spark plug leads and/or spark plug contacts. He certainly fixed the problem after replacing them, but I can't understand why such a problem would be temperature dependent?? A cheap and easy diagnosis though, apparently..