I recently acquired an 89 420 SEL. On cold start, the engine idles very roughly and the rpm fluctuates from about 500 to 1,100 in 5 sec. cycles until the engine reaches 80 degrees. It has 217,000 KM on it, about 160,000 miles. The maintenance history is unrecorded.

I'm starting with replacing the air and fuel filters. The fuel line had rusted through in one spot, but was patched using rubber gas line, no leaks. The previous owner also indicated that he had put in platinum plugs, which is yet to be confirmed. The timing chain probably has not been replaced, so it too, is on the to-do list. Valve seals have been replaced.

Any recommendations?

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1989 420 SEL