[mwebb]

average peak combustion pressure occurs at about 15 degrees after TDC
pressure does NOT increase after this time

so to answer the question :

nothing causes pressure to increase after combustion because pressure decreases after combustion
============================
now then
the current VW TDi (diesel) system does use a throttle body type flap
near the center of the exhaust to increase exhaust pressure to assist EGR at various times as determined by the ECM
and
the current VW TDi does have a throttle body type flap in the intake , again it is controlled by the ECM and part of it's function is to assist with EGR

both of these "throttle body" type flaps are drive by wire , there are no "throttle cables" or any mechanical connections to them , the ECM has control using little motors with position sensors on the flaps.

the EGR gas flows from a higher pressure area to a lower pressure area as assisted by the ECM

Originally Posted by George Tyler

the other thing, what causes the pressure to increase after combustion? The heat produced. Until combustion the pressure is higher, a similar amount of heat is produced, but as that heat is heating an increased mass of gas the temperature rise is reduced.