91 300te no pwr fm stop after warmup

'91 300te w/130000 miles.
starts very well on cold mornings. accelerates very well.
after ten minute/7 mi drive won't accelerate from stop. throttle seems to be sticking. after two or three times low, creeping acceleration engine seems to be more responsive but not as responsive as first start from cold in the morning.
any ideas on things to check.
nervous and frustrated.
i have had lots of old mercedes but this is the first time i have run into this problem.
thanks,
jerry green