96 E300d rough idle on cold startup.
 

Glow plug light started to flash so I had the mechanic change out the glow plugs and he changed out the fuel filter at the same time. Car has 87000 miles on it. Now on startup it idles rough and smokes, (never did this before) If I push down on the pedal and idle it up to 1500rpm it will smooth out, then runs fine. Any suggestions?