My 1981 380SLC has started idling and running very roughly when either hot or cold.

Starts immediately at all times.

Has twin row chain. 125k on engine. Fuel pump and filter changed 3k ago.

Any ideas would be welcomed - couldn't quite find something similar in the archives.

I'm wondering if it's a bad spark plug - is there a safe way of pulling these with the engine running to see if there's any change? Would it be OK to pull them at the distributor end? (The engine end is tough on a hot engine).