Don't over-look this part
http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2GN17VPXQ2GZ0RP5EF&yearid=1994%40%401994&makeid=MB%40%40MB%40%40X&modelid=E%2D420%2D001%40%40E+420+Sedan&catid=C%40%40Fuel+Injection&mode=PA&subcatid=C3000@@Fuel+Pressure+Regulator&source=www.peachparts.com&clientid=catalog.mercedesshop
It is a common failure part with age that will directly influence trims if it is leaking internally...the test is to take the vac line off and look for evidence of petro..there should be none. If there is, what happens is that raw gas gets sucked into the intake as UNMETERED fuel and the ECU can not correct w/o getting out of it's window frame %. So, code 19.
Takes 2 seconds to check and happens all the time. The best test is to run the car with the vac hose off for a few secs, as that will put the highest pressure on this part and if it is faulty, you will see fuel coming out the vac port.
Alway check that on fuel trims that have high adaptations/% and codes.