380SL Misfiring/ Loping idle?
 

1982 380SL and I suddenly have an issue with what I think is a misfire. I can't pin it down to just one cylinder though. It's kind of loping when at idle and I held the revs at 3000 and it does the same thing. The engine idles normal then rev dip then back go up very quickly and it cycles through this quickly.

I just redid the heads a couple hundred miles ago and replaced all the vacuum lines and it was running like it was new. This developed all the sudden a week ago. I've put new plugs in, new wires, cleaned the rotor and dist. cap and replaced the coil. I'm going to swap and old dist cap and rotor to see if that makes a difference.

I've checked all the vacuum lines and they are all still tight. At this point other than swapping the rotor and dist cap I'm running out of ideas. I wonder if it could be a clogged fuel injector or bad fuel? I put some cleaner in just in case but that hasn't made an effect yet. If the cap does't change anything I'm going to run through the troubleshooting section of the injector controller and see if that could be the issue.

Any thoughts or ideas is much appreciated.

Try the original coil. Is it OEM, or is it one of those "made in mexico" replacements? I had the same issue with my 380SL, I swapped out the new coil, with an old one from a 450SEL.

auxillary air valve was aways the issue on my 72 when those symptoms cropped up , not sure if the 82 has the same?

I finally resolved this issue. After running a full tank of gas through it, I pulled the plugs again and #2 was clearly not firing properly as compared to the other plugs. I did a compression test and sure enough, I wasn't getting compression on that cylinder. I pulled the valve cover and investigated the rocker arms. One of the rocker arm shims was somehow out of alignment. Must have been me when I was getting the rockers all shimmed properly. I filed to make it receive the rocker arm smoothly and reinstalled and now my issue is resolved! Thanks for the replies.

good work , I will stash that bit of info away in case I need it in the future.
do you mean the rocker arm -"arm" or where it rests