1989 S420 Missing bad at idle
 

I just changed the Fuel Filter and put in 8 new plugs, and ran two tanks of Fuel injector cleaner, but I still have a bad missing at or near idleing.
It runs smooth at 800 rpm and higher, and will fly to 100 mph on a clear interstate 10, but it struggles at idle. It's the same if the engine is cold or after running to the store and running for an hour. Sunday as I pulled into church it died, but restarted fine and I parked it. After church we went home and no problem running 10-70 mph, just misses at idle.
It starts fine, does not smoke at anytime. Give it a little gas and its fine.

$50 spent without any improvement.

What should I check next?

Thanks