[W126 Coupe] 560 SEC hiccups

[Jay Hirsch]

I know this was discussed  recently

Yesterday went  on a 280 mile trip, 75 mph with my 1990 560SEC.  Also  
got 19 mpg

Got gas  twenty minutes from my home, where I usually get gas for all  
my cars.
Five minutes after getting gas car started to have a  "hiccup" or  
slight miss while stopped for traffic  light.

Light  changed, give  the car  gas and runs fine.  Come to stop and   
car idles  a little rough,  slight miss.  almost seems to want to  
conk out.

Will point until I got gas car was cruisin between 70-80 mph,  all  
highway driving

Same thing today, once  the car warmed up car idles rough with  
slight  surge up and down,
Give the car gas, pedal to metal and runs OK

What sensors, vacuum line or relay should  I be looking at?
thank you
keep cruisin
Jay H