Sounds like the control pressure/warmup regulator is causing a lean mixture when cold.

There is a small strainer in the return line from the regulator which blocks up and can cause hesitation and rough running when cold. Try cleaning that first. Otherwise get some fuel gauges and check all your pressures before throwing parts at it, it may be the regulator though.

__________________
Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32