Hi, The first code indicates a problem with the electronic throttle on the engine
The second is a misfire on cylinder 1, which may or may not be currently happening.
For the p1542 fault bmw issued a service bulletin on 2/99 for this issue.
They advised technicians to check the wiring from the engine computer to the MDK electronic throttle on the engine. If the wiring checks out ok, then the throttle needs to be replaced.
In most cases on this particular engine, this fault indicates the throttle is simply bad.
It has potentiometers inside which measure position of the throttle, when these fail to read correctly the engine computer will go into failsafe mode, and have reduced power.
I would try and source a known good used one, or a new throttle, have it installed.
Then with a bmw scan tool, clear all the throttle adaptations. This should fix the problem.
After this is done, you'll need to check if the misfire fault returns or not, it could also need spark plugs or an ignition coil.
The throttle part # XXXXX XXXXX 54 1 433 414