One thing is for sure, the california models get worse gas milege than Federal versions. I don't know exactly why this is, but its true. I think it MAY have something to do with gearing since my car runs around 3500rpm+ ove 70, which is higher than most people pull at that speed.

Additionally, the '84 cali version has what is called an "air recirculation valve" on the intake manifold. No one seems to know exactly what purpose these serve, but it obviously has something to do with emissions. I think all 617 engines have this valve for '85. On mine it made a very annoying wistling noise, and I disconnected it with no ill affect. Additionally, for '85 california models had a large canister air filter that was installed in the front corner next to the radiator. I think the was because MB needed room for the trap oxidizer, but I'm not exactly sure if '85 cali-version 617 engines had a trap oxidizer. I know for sure that '85 Federal versions do not have a trap oxidizer and have the air filter on top like all other 617 engines.

Also, some '84 and '85 cars had a different PCV set up. They had a tube that ran down to the "U" shaped plastic tube that runs from the air filter to the turbo and a tube connected to that line that runs to the bottom side of the air filter. I don't know the reason for this setup.

The '84 and '85 Cali versions also have more vacuum plumbing to operate the air recirculation and EGR valves. The '85s have different vaccum plumbing than the '84s. This system is operated by an electronic control module that is installed in the passenger side kick-panel. This module also operates the tachometer (which is probably why my car doesn't have the typical tachometer failure other w123 owners experience).

Lastly, these cars do not have the vaccum operated transmission modulator on top of the valve cover. My car has no modulator, electric switches, nothing - just the bowden cable and a vaccum line that runs from the back of the injector pump.

Thats all I can tell you from my personal experience. I'm no expert, so if anyone else has info, please chime in.

Greg
'84 300D, 170k