Thanks for the input DG.
Neither of the cars is California.
There must have been a change in the engine management system from 1989 to 1990, The donor engine, from the 1990 300E had an EGR valve, but no thermo vac valve on the top of the head, and my 1989 300SEL was just he opposite. When I swapped engines I had install the 1989 the thermo vac valve into the 1990 head. I also had to plug the EGR vacuum line at the intake manifold. There was also a significant difference as my 1989 had no smog/air pump and the 1990 did. I actually had to plug a small exhaust hole in the head that fed into the pump.
Good idea on the Performance site. I’ve bought some parts from those guys before, I’ll have a look.
Thanks Again.