i think i have some sort of engine management problem.
99% of the time the engine behaves fine but sometimes when pulling away from statonary the engine goes flat and you get no acceleration at all.this only seems to happen in stop start traffic and will then work ok the next time you pull away.
i'm guessing this could be a faulty throttle sensor.
the van has done 70000 miles
don`t guess,it could cost you a small fortune,find out when your filters were done last and think about seeing if there are any fault codes stored,is it overheating when in traffic?any management lights on?